Onium salts improve the kinetics of photopolymerization of acrylate activated with visible light

The aim was study the influence of onium salts on the kinetics of photopolymerization in the visible light region. Trimethylolpropane triacrylate TMPTA was selected as a monomer, and activated by 1,3-bis(phenylamino)squaraine (SQ) used as a photosensitizer in addition to tetramethylammonium n-butyltriphenylborate (B2). The iodonium salt [A–I–B]⁺X⁻ functioned as a second radical initiator, bearing a different substitution pattern for the cation. The ternary system was formulated with different concentrations of both borate and diphenyliodonium salts. Differential scanning calorimetry was used to investigate the polymerization reaction over the photoactivation time carried out at 300 nm < λ < 500 nm irradiation. When the squaraine dye/borate salt was used as photoinitiator, a slow polymerization reaction was observed and a lower monomer conversion. The addition of a third component (onium salt) increased the polymerization rate and conversion. Ternary photoinitiator systems showed improvement in the polymerization rate of triacrylate leading to high conversion in a short photoactivation time. The photoinitiating ability of bi- and tri-component photoinitiators acting in the UV-Vis region for initiation polymerization of triacrylate was compared with those of some commercially used photoinitiating systems. It was also found, that, the parallel electron transfer from an excited state of the sensitizer to [A–I–B]⁺X⁻, and an electron transfer from a ground state of R(Ph)₃B⁻N(CH₃)₄⁺ to an excited state of the sensitizer results in two types of initiating radical.

The chemical mechanisms were investigated by steady state photolysis and nanosecond laser flash photolysis experiments. A mechanism for initiating polymerization using both onium salts is proposed here.     

New,highly versatile bimolecular photoinitiating systems for free-radical,cationic and thiol–ene photopolymerization processes under low light intensity UV and visible LEDs for 3D printing application

1-Amino-4-methyl-naphthalene-2-carbonitrile derivatives are proposed for the role of photosensitizers of iodonium salt during the photopolymerization processes upon near UV-A and visible ranges. Remarkably, 1-amino-4-methyl-naphthalene-2-carbonitrile derivatives are highly versatile allowing access to photoinitiating systems for (i) the cationic photopolymerization of epoxide monomers with a ring opening mechanism and vinyl ether monomers with chain growth mechanisms (ii) the free-radical photopolymerization of acrylate monomers, (iii) the photopolymerization of interpenetrated polymer networks (IPNs) based on epoxide and acrylate monomers under air and under laminate in an oxygen-free atmosphere (iv) the thiol–ene photopolymerization processes. Excellent polymerization profiles are obtained during all types of photopolymerization processes. The initiation mechanisms are analyzed through steady state photolysis, cyclic voltammetry and fluorescence experiments. Moreover, the newly developed bimolecular photoinitiating systems were investigated by applying an additive manufacturing process under visible light sources. Furthermore, vat photopolymerization processes using IPN compositions, which are polymerizable by using new photoinitiating systems, provide high resolution and speeds. For these reasons, new bimolecular photoinitiating systems are promising initiators for photopolymerization-based 3D printing process to fabricate 3D structures.

1-Amino-4-methyl-naphthalene-2-carbonitrile derivatives are proposed for the role of photosensitizers of iodonium salt during the photopolymerization processes upon near UV-A and visible ranges.     

A new safranin based three-component photoinitiating system for high resolution and low shrinkage printed parts via digital light processing

Additive manufacturing or 3D printing has attracted the interest of researchers in industry and academia because of its outstanding features. In this study, a new three-component photoinitiating system (PIS) consisting of safranin O (SFH⁺), thiol derivatives and diphenyl iodonium salt was used for the free radical photopolymerization of a diacrylate monomer (SR349) in DLP 3D printing. The photoinitiating characteristics of this PIS were evaluated and advantageously compared to those of a conventional PI (TPO) by using RT-FTIR. It is shown that the proposed PIS could be used as an efficient PIS for free radical photopolymerization. In addition, the resolution and shrinkage of printed parts in the presence of this three-component PIS were measured and compared to those printed using TPO as a photoinitiator. The resolution of printed parts was determined by using SEM and profilometry techniques. In addition, photorheometry was used to evaluate the linear shrinkage of samples. Moreover, the initiating mechanism of the three-component PIS was studied by using laser flash photolysis (LFP). A photocyclic mechanism was outlined for the three-component PIS which demonstrated this mechanism would be very beneficial for DLP 3D printing.

The resolution and shrinkage of DLP 3D printed parts improve remarkably when SFH⁺/RSH/IOD⁺ is used as a photoinitiating system.     

Mild polyaddition and polyalkylation based on the carbon–carbon bond formation reaction of active methylene

The Michael addition and alkylation reaction of active methylene compounds (AMCs) with two active hydrogens had been investigated extensively in organic chemistry, while the polymerization of AMCs had few studies. Herein, we reported active methylene-based polyaddition and polyalkylation catalyzed via an organic superbase under ambient conditions. A model polymerization was first conducted between ethylene glycol diacrylate (EGDA) and methyl cyanoacetate (MCA). The molecular weight (M_w) of the model polymer was up to 50 500 g mol⁻¹ with a high yield (99%). Eight AMCs were selected and a high-throughput parallel synthesizing instrument (HTPSI) was used to synthesize semi-library polymers of AMCs and EGDA via a Michael type polyaddition. The obtained AMC-based polymers had low cell cytotoxicity. Elastomers with cyanogen groups could be prepared using trimethylolpropane triacrylate (TMPTA) as a crosslinker. Furthermore, three dihalogen compounds were explored to polymerize with MCA and malononitrile via alkylation reactions. The pendent cyanogen or ester groups of the polymers could be reduced by lithium aluminum hydride. Novel polymer families were constructed based on the polyaddition and polyalkylation of AMCs.

Active methylene-based polyaddition and polyalkylation catalyzed via an organic superbase were studied in a high-throughput parallel synthesizing instrument.     

Preparation of environmentally friendly acrylic pressure-sensitive adhesives by bulk photopolymerization and their performance

Polyacrylic pressure-sensitive adhesives (PSAs) based on butyl acrylate (BA), 2-hydroxyethyl acrylate (HEA), and acrylic acid (AA) were prepared by a bulk polymerization process triggered by a radical photoinitiator under UV irradiation and UV-crosslinking. 1,6-Hexanediol diacrylate (HDDA) with difunctional groups was introduced into the PSAs to modify semi-interpenetrating network structures. The effect of HDDA content on the pressure-sensitive performance was comprehensively tested. The viscosity of the prepolymer was measured by a rotational viscometer. Prepolymers obtained by a photoinduced process and UV crosslinking process were confirmed via Fourier transform infrared spectroscopy (FTIR). All double bonds participated in the copolymerization without any remaining monomers, which reflected the concept of green environmental protection. Gel content in the crosslinked portion was examined by Soxhlet extraction, whilst the soluble molecular weight of PSAs was characterized by gel permeation chromatography (GPC). The viscoelastic properties of polymer films were determined by dynamic mechanical analysis (DMA). The T_g value and storage modulus (G′) of the PSAs were enhanced with the addition of HDDA. Moreover, three fundamental adhesive properties, i.e. loop tack force, peel force and shear strength of PSAs, were measured. The results showed that UV crosslinking technology achieved a good balance of the three forces with excellent pressure-sensitive properties.

Polyacrylic pressure-sensitive adhesives based on butyl acrylate, 2-hydroxyethyl acrylate, and acrylic acid were prepared by a bulk polymerization process triggered by a radical photoinitiator under UV irradiation and UV-crosslinking.     

Structural effect of oxazolone derivatives on the initiating abilities of dye-borate photoredox systems in radical polymerization under visible light

Three photoinitiating systems based on new oxazolone derivatives have been developed and their performance in initiation of radical polymerization of acrylate monomers has been tested by differential scanning calorimetry. The absorption characteristics of the oxazol-5(4H)-ones is compatible with the emission characteristics of different light sources like diode pulse solid state lasers. Thus, the dyes were used as sensitizers which are photoreduced during a photochemical reaction in the presence of phenyltriethylborate salt. Results showed that the increase in the dimensionality of the molecule extends the range of light absorption and increases the efficiency of the photoinitiation process. The photoreduction of the oxazolone–borate complex was studied using steady-state and nanosecond laser flash photolysis. The dye singlet and triplet were found to be quenched by the electron donor via an electron transfer process. Rate constants for the quenching of the excited states were high and were found to depend on the dye structure.

Three photoinitiating systems based on new oxazolone derivatives have been developed and their performance in initiation of radical polymerization of acrylate monomers has been tested by differential scanning calorimetry.     

Maleimide end-functionalized poly(2-oxazoline)s by the functional initiator route: synthesis and (bio)conjugation

The synthesis of poly(2-ethyl-2-oxazoline)s with a maleimide group at the α chain end was carried out from new sulfonate ester initiators bearing a furan-protected maleimide group. The conditions of the polymerization were optimized for 50 °C using conventional heating (in contrast to microwave irradiation) to counteract the thermal lability of the cycloadduct introduced to protect the maleimide double bond. At this temperature, a tosylate variant was found to be unable to initiate the polymerization after several days. The controlled polymerization of 2-ethyl-2-oxazoline with a nosylate derivative was, however, successful as shown by kinetic experiments monitored by gas chromatography (GC) and size-exclusion chromatography (SEC). Poly(2-ethyl-oxazoline)s of various molar masses (4500 < M_n < 12 000 g mol⁻¹) with narrow dispersity (Đ < 1.2) were obtained. The stability of the protected maleimide functionality during the polymerization, its deprotection, and the reactivity of the deprotected end group by coupling with a model thiol molecule were proven by ¹H NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). Finally, the conjugation of maleimide-functionalized poly(2-oxazoline) to a model protein (bovine serum albumin) was demonstrated by gel electrophoresis and MALDI-ToF mass spectrometry.

A new route for the synthesis of polyoxazolines with a maleimide end group is reported using a functional initiator.     

Ionic conductivity enhancement in solid polymer electrolytes by electrochemical in situ formation of an interpenetrating network

Various overoxidized poly(1H-pyrrole) (PPy), poly(N-methylpyrrole) (PMePy) or poly(3,4-ethylenedioxythiophene) (PEDOT) membranes incorporated into an acrylate-based solid polymer electrolyte matrix (SPE) were directly electrosynthesized by a two-step in situ procedure. The aim was to extend and improve fundamental properties of pure SPE materials. The polymer matrix is based on the cross-linking of glycerol propoxylate (1PO/OH) triacrylate (GPTA) with poly(ethylene glycol) diacrylate (PEGDA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a conducting salt. A self-standing and flexible polymer electrolyte film is formed during the UV-induced photopolymerization of the acrylate precursors, followed by an electrochemical polymerization of the conducting polymers to form a 3D-IPN. The electrical conductivity of the conducting polymer is destroyed by electrochemical overoxidation in order to convert the conducting polymer into an ion-exchange membrane by introduction of electron-rich groups onto polymer units. The resulting polymer films were characterized by scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, differential scanning calorimetry, thermal analysis and infrared spectroscopy. The results of this study show that the combination of a polyacrylate-matrix with ion selective properties of overoxidized CPs leads to new 3D materials with higher ionic conductivity than SPEs and separator or selective ion-exchange membrane properties with good stability by facile fabrication.

Conductive polymers were encapsulated and subsequently overoxidized in an acrylate polymer matrix as potential separator materials via the combination of UV-induced and electrochemical polymerization.     

Large-scale transfer of Ag nanowires from PET to PC film using a roll-to-roll UV lamination process for a capacitive touch sensor

Demand for flexible transparent sensors for futuristic cars is increasing since such sensors can enhance the freedom of design and aesthetic value in the interior of cars. Herein, we propose a unique roll-to-roll UV lamination process that can expedite large-scale Ag nanowire (AgNW) transfer for a flexible capacitive sensor, using a photocurable resin composed of an epoxy acrylate oligomer, a reactive monomer (1,6-hexanediol diacrylate), and a photoinitiator (1-hydroxycyclohexyl phenyl ketone). The acryl groups in the resin were rapidly crosslinked by UV irradiation, which facilitated the AgNWs transfer from a PET to a PC substrate with the speed of 1050 cm² min⁻¹ and enhanced the adhesion between the AgNWs and the PC substrate. Systematic experiments were performed to determine optimal fabrication parameters with respect to the UV dose, lamination pressure, and laser dicing conditions. At the optimal fabrication conditions, the sheet resistance of AgNWs on a PC film (PC-AgNW) was as small as 36.79 Ω sq⁻¹, which was only 3.17% deviation from that on a PET film (PET-AgNW). Furthermore, the optical transmittance of the PC-AgNW exceeded 88% over the visible range, and it was greater than that of the PET-AgNW. Notably, the sheet resistance of the PC-AgNW was almost constant after 50 taping and peeling cycles, indicating remarkable adhesion to the substrate. Furthermore, a capacitive touch sensor was fabricated using the PC-AgNW, and its switching signals were presented with and without finger touch.

We proposed a unique roll-to-roll lamination process that can facilitate the transfer of Ag nanowires (AgNWs) from one flexible substrate (PET substrate) to another (PC substrate) for a capacitive touch sensor.     

Improved phase purity and film quality in quasi-2D perovskite light-emitting diodes by an additive with the trimethacrylate group

Quasi-2D perovskites are potential materials for optoelectronics like light-emitting diodes (LEDs); compared to their 3D counterparts, they are considered more stable against the atmosphere and more efficient in exciton confining. However, the simultaneous formation of different phases in the quasi-2D perovskite film, i.e., the phase impurity issue, lowers the device performance. We propose using a small molecule additive, trimethylolpropane trimethacrylate (TMPTA), to suppress the phase impurity by mixing it into the antisolvent. The phase pure quasi-2D perovskite film was obtained, and meanwhile, the film quality was also improved. Moreover, the ester functional groups in TMPTA also passivate the charged defects in the perovskite film, minimizing the carrier recombination in the device. Correspondingly, with TMPTA modification, the maximum current efficiency is increased by 25%, and the half lifetime of the PeLEDs is prolonged by three times.

By adding TMPTA to the anti-solvent, the phase purity of the perovskite and the performance of the device are improved.     

Light and magnetism dual-gated photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization

A novel raspberry-like γ-Fe₂O₃@carbon dot (CD) nanocatalyst was prepared and applied for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization. The nanocatalyst was found to be an efficient photocatalyst in visible light-regulated PET-RAFT polymerization owing to the oxidative quenching mechanism between the photoexcited γ-Fe₂O₃@CDs and the RAFT agent in the PET process. Notably, polymerization can be reversibly ceased in the absence of light or under an external magnetic field. The superparamagnetic nature and high saturation magnetization value (∼30.4 emu g⁻¹) of the nanocatalyst contribute to convenient recycling of the nanocatalyst after polymerization. The PET-RAFT polymerization with the nanocatalyst before and after recycling was investigated, which displayed all the characteristics of controlled/living polymerization systems.

PET-RAFT polymerization can be reversibly ceased in the absence of light or under an external magnetic field with a novel raspberry-like γ-Fe₂O₃@CD nanocatalyst.     

Kinetic study of polydopamine sphere synthesis using TRIS: relationship between synthesis conditions and final properties

The synthesis and characterization of polydopamine (PDA) using dopamine (DA) as the monomer and (hydroxymethyl)aminomethane (TRIS) as the oxidant is studied. The effect of temperature and TRIS concentration on the kinetics of dopamine polymerization is evaluated, and the kinetic parameters are also calculated. Three TRIS concentrations are used to assess their effect on DA polymerization kinetics. The reaction at 1.5 mmol of TRIS shows a sustained increase of the rate constant with temperature from 2.38 × 10⁻⁴ to 5.10 × 10⁻⁴ when the temperature is increased from 25 to 55 °C; however, not all reactions follow an Arrhenius law. In addition, the correlation between the synthesis parameters and morphological, structural, and thermal properties of polydopamine is established. The morphology of the PDA particles is evaluated by Scanning Electron Microscopy (SEM), the relationships between the diameter, distribution size, and the rate constant. Thermal characterization by Differential Scanning Calorimetry (DSC) shows an endothermic transition around 130 °C associated with the melting of PDA''s regular structure. It is supported by structural studies, such as infrared and Raman spectroscopy and X-ray Diffraction (XRD), by observing a broad peak at 23.1° (2θ) that fits with a graphitic-like structure of PDA.

Synthesized PDA shows unexpected regular structure giving crystallinity. Kinetic parameters for spherical PDA are reported showing that polymerization depends upon TRIS concentration and temperature.     

Synthesis and characterization of magnetic chitosan microspheres for drug delivery

A novel magnetic microsphere was prepared by simple microemulsion polymerization for protein drug delivery systems. The Fe₃O₄ magnetic nanoparticles were successfully encapsulated in chitosan microspheres, which endowed the chitosan microspheres with good magnetism. The drug loading performance results indicated that the prepared magnetic chitosan microspheres exhibited a superior drug loading capacity, and the drug loading amount reached 947.01 mg g⁻¹. Furthermore, the magnetic chitosan microspheres also showed a higher drug release rate (87.8%) and evident sustained-release performance in vitro. The magnetic microsphere carrier will be widely used in the biomedical field as a promising drug carrier.

A novel magnetic microsphere was prepared by the simple microemulsion polymerization for protein drug delivery systems. This magnetic microsphere exhibited good magnetism and superior drug loading capacity and evident sustained-release performance.     

Enzymatic synthesis of biobased aliphatic–aromatic oligoesters using 5,5′-bis(hydroxymethyl)furoin as a building block

5,5′-Dihydroxymethyl furoin (DHMF) is a novel biobased difuranic polyol scaffold, achievable from the benzoin condensation of 5-hydroxymethylfurfural (HMF), which has recently been employed as a monomer for the preparation of cross-linked polyesters and polyurethane. Its upgrading by means of enzymatic reactions has not yet been reported. Here we demonstrated that Candida antarctica lipase B (CALB) is a suitable biocatalyst for the selective esterification of the primary hydroxyl groups of DHMF. Exploiting this enzymatic activity, DHMF has been reacted with the diethyl esters of succinic and sebacic acids obtaining fully biobased linear oligoesters with number-average molecular weight around 1000 g mol⁻¹ and free hydroxyl groups on the polymer backbone. The structures of the DHMF-diacid ethyl ester dimers and of the oligomers were elucidated by NMR and MS analyses.

Fully bio-based linear oligoesters were obtained by the unprecedented enzymatic polymerization of 5,5′-bis(hydroxymethyl)furoin with succinic and sebacic acid diethyl esters.     

The design and synthesis of high efficiency adsorption materials for 1,3-propanediol: physical and chemical structure regulation

In this study, a series of polystyrene-divinylbenzene resins with precise physical structure regulation and chemical modification were successfully synthesized. The regulation of Friedel–Crafts reaction conditions resulted in several physical resins with various BET surface areas and pore structures, while the adsorption of 1,3-propanediol revealed that the molecular size and other physical properties exhibited a moderate contribution to the adsorption of hydrophilic compounds. The adsorption processes between 1,3-propanediol and nitrogen, oxygen and boron functional group modified resins were further explored, and boronic acid modified resins named PS-3NB and PS-SBT exhibited higher adsorption capacities than commercial resin CHA-111. The adsorption capacity of PS-3NB and PS-SBT reached 17.54 mg g⁻¹ and 17.23 mg g⁻¹, respectively, which were 37% and 35% higher than that of commercial resin CHA-111. Furthermore, the adsorption mechanism demonstrated that the content of boronic acid, solution pH and adsorbate hydrophobicity were the primary adsorption driving forces. Herein, we provided a method to modify polystyrene-divinylbenzene materials with boronic acid to selectively adsorb hydrophilic polyols via the specific affinity between boronic acid and diol molecule.

Chemically modified materials efficiently captured 1,3-propanediol via the specific affinity between boronic acid and diol.     

Intermolecular interactions of an isoindigo-based organic semiconductor with various crosslinkers through hydrogen bonding

Three crosslinkers (1,4-diaminobutane, 1,8-diaminooctane, and 1,6-hexanediol) were selected to produce hydrogen-bonded networks using a simple and effective method. The effects of these crosslinkers on the arrangement of crystalline structures were successfully studied using X-ray diffraction and high-voltage electron microscopy. The hydrogen-bonded isoindigo-based small molecules with 1,4-diaminobutane showed the best performance, with a crystal structure showing long-range order, due to the more suitable length of the 1,4-diaminobutane chain. The hole mobility estimated from hole-only devices based on isoindigo was enhanced from 1.24 × 10⁻⁶ cm² V⁻¹ s⁻¹ to 7.28 × 10⁻⁴ cm² V⁻¹ s⁻¹ as a result of the inclusion of this crosslinker, due to the formation of stronger interactions between the molecules.

The effects of crosslinkers, functioning via hydrogen bonding, on controlling the arrangement of molecules were investigated. The hole mobility of hydrogen-bonded organic materials displaying long-range order was significantly enhanced.     

Solvent extraction of rare earths elements from nitrate media in DMDOHEMA/ionic liquid systems: performance and mechanism studies

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and two ionic liquids (ILs) (1-ethyl-1-butylpiperidinium bis (trifluoromethylsulfonyl)imide [EBPip⁺] [NTf₂⁻] and 1-ethyl-1-octylpiperidinium bis (trifluoromethylsulfonyl)imide [EOPip⁺] [NTf₂⁻]). Using the extractant N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), the effect of pH was investigated in detail to recover extraction mechanisms. The use of ILs as the organic solvent instead of n-dodecane, greatly enhances extraction efficiency, and an ionic liquid with a shorter alkyl chain [EBPip⁺] [NTf₂⁻] provides higher extraction than [EOPip⁺] [NTf₂⁻]. The mechanistic study points out that for low nitric acid concentrations ([HNO₃] ≤ 0.01 M), metal is extracted via a cation of the ionic liquids, while for higher nitric acid concentrations ([HNO₃] ≥ 1.0 M), extraction occurs through pure solvation mechanism of DMDOHEMA as in conventional diluents. This latter case is of high interest for applications, as higher extraction can be obtained without any loss of ILs by ion exchange mechanisms.

Extraction of La(iii), Eu(iii) and Fe(iii) was compared in n-dodecane and in two ionic liquids (ILs) [EBPip⁺] [NTf₂⁻] and [EOPip⁺] [NTf₂⁻]. Extraction mechanisms have been investigated as a function of pH.     

Free-standing polydopamine films generated in the presence of different metallic ions: the comparison of reaction process and film properties

Polydopamine is widely used in surface modification, nanofiltration, photonic devices and drug delivery. The formation mechanism and properties of polydopamine are modified by the experimental conditions. Herein we demonstrated a comparison study of free-standing polydopamine films generated at the air–solution interface and their corresponding nanoparticles in solutions, in the presence of various metallic cations, Na⁺, Ca²⁺, Mg²⁺ and Co²⁺. Adding metallic ions influenced the intermediates in dopamine polymerization, and in turn the morphology and properties of the produced free-standing polydopamine films. Moreover, we observed that the polymerization process accompanying the stratification determines the formation of free-standing films at the air–solution interface: the fast polymerization of dopamine in a Co²⁺ environment leads to a rugged film surface and porous film body, whereas the comparatively slow polymerization of dopamine under conditions of other metallic ions results in a smooth and solid film. In addition, the water contact angles of the upper and lower surface of the polydopamine films were different. This investigation enriches our knowledge of dopamine polymerization in different environments, which is particularly useful for further application of free-standing polydopamine films.

Different stratification processes lead to different morphologies of films generated with various cations.     

Towards sustainable diagnostics: replacing unstable H2O2 by photoactive TiO2 in testing systems for visible and tangible diagnostics for use by blind people

Blind and color blind people cannot use colorimetric diagnostics; the problem is especially severe in rural areas where high temperatures and the absence of electricity challenge modern diagnostics. Here we propose to replace the unstable component of a diagnostic test, H₂O₂, with stable TiO₂. Under UV irradiation, TiO₂ forms reactive oxygen species that initiate polymerization of acrylamide causing liquid-to-gel transition in an analyte-dependent manner. We demonstrate that specific DNA sequences can be detected using this approach. This development may enable the detection of biological molecules by users with limited resources, for example in developing countries or for travelers in remote areas.

Blind and color blind people cannot afford colorimetric diagnostics; the problem is especially severe in rural areas where high temperatures and the absence of electricity challenge modern diagnostics.

An ideal diagnosis, including diagnosis for infectious diseases, should meet the ASSURED criteria: (i) affordable by those at risk of infection; (ii) sensitive; (iii) specific; (iv) user-friendly; (v) rapid, and robust, for example not requiring refrigerated storage; (vi) equipment-free; (vii) delivered to those who need it.¹Analytic methods with visually detectable outputs (e.g. color change) satisfy criteria (iv) and (vi), and are therefore among the most common. Indeed, pregnancy tests, test strips for measuring acetone and glucose in urine for diabetic people, and pH strips are known to be the best to make the analysis easiest in data output. However, such methods cannot be used by the visually impaired.Recently, we described an alternative output signal that cannot only be detected by sight, but also by touch and applied it in the detection of adenosine triphosphate (ATP) and deoxyribonucleic acid (DNA).² The method is based on the analyte-dependent radical polymerization of acrylamide into polyacrylamide in the presence of hydrogen peroxide (H₂O₂). H₂O₂ serves as a source of radicals. The test uses affordable reagents and does not require any instrumentation for signal readout. Such test systems can be adopted for detection of a wide variety of biological analytes. Unfortunately, H₂O₂ is subject to light decomposition and should be refrigerated for long term storage; it is also prone to exploding at high concentrations. Therefore, substituting H₂O₂ with a more stable ingredient would increase the shelf life of the test system and make it usable in those environments with limited access to refrigeration. This work is devoted to addressing the ASSURED criterion (v): we substituted perishable H₂O₂ with stable titania (TiO₂) as an alternative source of initiators of radical polymerization.Recently we demonstrated the possibility of converting electromagnetic energy into pH gradients³ or generating reactive oxygen species (ROS) using TiO₂,^3,4 which makes this approach attractive for controlling interactions between chemical networks. Moreover, combining several functional chemical networks can result in a network with new functions. We have also shown that the pH gradient on titania can be used for regulating enzymatic reaction networks.⁵ In this work, we were interested in using photogenerated ROS (such as superoxide anion O₂˙⁻, hydroxyl radical ˙OH, and hydrogen peroxide H₂O₂) (Fig. 1) to initiate radical polymerization with the aim of making a visual and tactile portable sensor for the detection of biologically important molecules (DNA, RNA, ATP). Under ultraviolet (UV) irradiation, TiO₂ splits water, which results in the generation of a high concentration of ROS and free radicals.⁶Open in a separate windowFig. 1(i) A portable sensor based on a light-induced liquid-to-gel transition for polymer by radical polymerization on TiO₂ particles. The details of the sensor design are shown in Fig. 5; (ii) ROS formation on titania via reactions with photogenerated photohole (h⁺) and photoelectron (e⁻).The sensing system is based on deoxyribozyme sensor that produces ROS in the presence of a specific analyte, thereby triggering the radical polymerization of acrylamide into polyacrylamide. The buffer contained acetylacetone, H₂O₂, 40% acrylamide/bisacrylamide, hemin and a split deoxyribozyme sensor with peroxidase-like activity (PxR).² In the presence of the specific analyte sequence (A1 in this study), the sensor hybridized with the analyte and formed PxR, which bound hemin and decomposed H₂O₂ to ROS. The latter oxidized acetylacetone to the acetylacetone radical, which initiated the polymerization of acrylamide, resulting in liquid-to-gel conversion. Here, the aim of the research is to increase the system sustainability by changing H₂O₂ to TiO₂ particles. Noteworthy is that the system is externally controlled by UV light, since TiO₂ produces ROS only upon irradiation.Firstly, we quantified the TiO₂-derived ROS with the aim of finding the optimal conditions for the generation of the minimum amount of ROS needed for the polymerization. We used luminol chemiluminescence (CL) calibrated with hydrogen peroxide. Luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) is a widely used CL reagent and has CL emission at different wavelengths depending on the conditions.⁶ Traditionally, luminol CL is observed in the presence of H₂O₂ in alkaline solutions (Fig. 2), which is catalyzed by metal ions, metal complexes or vitamins.^7–10Open in a separate windowFig. 2Mechanism of chemiluminescence of luminol and O₂⁻˙.The luminol CL signaling is conveniently used for the detection of ROS (particularly superoxide anion, hydrogen peroxide, hydroxyl radical) in biological systems.^11–16Irradiation of TiO₂ suspensions of different concentrations (0.03 M and 0.06 M) at two wavelengths (365 nm and 254 nm) revealed more ROS being formed upon irradiation at 254 nm – as was expected (Fig. 3).Open in a separate windowFig. 3Log concentration of ROS generated in TiO₂ suspensions of different concentration (0.03 M and 0.06 M) under irradiation by UV light with different wavelengths vs. irradiation time.According to the data obtained, the minimum concentration of TiO₂ needed to trigger polymerization after 5 min of irradiation at 365 nm was 1.25 mM (Fig. 4). We therefore used these conditions in the following experiments, since short irradiation time and longer wavelength of UV-A irradiation are less damaging to the DNA-based biosensor component than UV-C light with wavelength of 254 nm. It should be noted that control experiments were made without TiO₂ particles and polymerization did not occur. Next, we optimized the conditions for the analyte-dependent activation of PxR resulting in acrylamide polymerization. If polymerization occurs, the gel will stick to the bottom of the inverted tubes (Fig. 5).² To demonstrate the general applicability of the approach, we designed a sensor for an analyte of biomedical significance, nucleic acids, as an example. A sequence of 16S rRNA, which was represented in this study by synthetic A1 sequence (5′-CAT TAC TCA CCC GTC CGC CAC TCG TCA GCG AAG CAG CAA GCT GCT TCC TGT TAC CGT TCG), of pathogenic E. coli O157:H7 was chosen as the target analyte,. The binding of A1 to PxR1 and PxR2 stabilized the G-quadruplex structure, which then binds to hemin and catalyzes the polymerization (Fig. 5A).Open in a separate windowFig. 4The dependence of the log concentration of ROS generated on TiO₂ particles on TiO₂ suspension concentration. Inserts show the minimum concentration of TiO₂ particles in a suspension (therefore minimum concentration of ROS generated on TiO₂ particles), needed for the gel formation.Open in a separate windowFig. 5Polymerization-based visual and tactile detection of A1 analyte. (A) Sensor design: RNA strands PxR1 and PxR2 bind A1 sequence and form a G-quadruplex structure, which then binds to hemin (green oval) and catalyzes the radical polymerization of the acrylamide solution. The dotted lines represent triethylene glycol linkers. (B and C) Inverted test-tubes with radical polymerization of acrylamide initiated by reactive oxygen species generated on TiO₂ particles under UV light 365 nm. (B) Systems with different concentrations of hemin (

Determination of chloropropanol with an imprinted electrochemical sensor based on multi-walled carbon nanotubes/metal–organic framework composites

In this paper, a composite composed of carboxylated multi-wall carbon nanotubes (cMWCNT) incorporated in a metal–organic framework (MOF-199) has been synthesized using 1,3,5-benzoic acid as a ligand through a simple solvothermal method. The synthesized cMWCNT/MOF-199 composite was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometry (XRD). The cMWCNT/MOF-199 hybrids were modified on the surface of glassy carbon electrodes (GCE) to prepare a molecularly imprinted electrochemical sensor (MIECS) for specific recognition of 3-chloro-1,2-propanediol (3-MCPD). The electrodes were characterized by differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Under optimal conditions, the electrochemical sensor exhibited an excellent sensitivity and high selectivity with a good linear response range from 1.0 × 10⁻⁹ to 1.0 × 10⁻⁵ mol L⁻¹ and an estimated detection limit of 4.3 × 10⁻¹⁰ mol L⁻¹. Furthermore, this method has been successfully applied to the detection of 3-MCPD in soy sauce, and the recovery ranged from 96% to 108%, with RSD lower than 5.5% (n = 3), showing great potential for the selective analysis of 3-MCPD in foodstuffs.

In this study, cMWCNT/MOF-199 composites were used as the modified electrodes, and a MIECS having specific recognition of 3-MCPD was prepared by electrochemical polymerization for selective analysis of 3-MCPD in foodstuffs.