Towards cancer diagnostics – an α-feto protein electrochemical immunosensor on a manganese(iv) oxide/gold nanocomposite immobilisation layer

A novel electrochemical immunosensor for the quantification of α-feto protein (AFP) using a nanocomposite of manganese(iv) oxide nanorods (MnO₂NRs) and gold nanoparticles (AuNPs) as the immobilisation layer is presented. The MnO₂NRs was synthesised using a hydrothermal method and AuNPs were electrodeposited on a glassy carbon electrode surface. The MnO₂NRs were characterised with scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray powder diffraction (XRD). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterise the immunosensor at each stage of the biosensor preparation. The MnO₂ nanorods and AuNPs were applied as the immobilisation layer to efficiently capture the antibodies and amplify the electrochemical signal. Under optimised conditions, the fabricated immunosensor was utilised for the quantification of AFP with a wide dynamic range of 0.005 to 500 ng mL⁻¹ and detection limits of 0.00276 ng mL⁻¹ and 0.00172 ng mL⁻¹ (S/N = 3) were obtained from square wave anodic stripping voltammetry and EIS respectively. The nanocomposite modifier enhanced the immunosensor performance. More so, this label-free immunosensor possesses good stability over a period of two weeks when stored at 4 °C and was selective in the presence of some interfering species.

A novel electrochemical immunosensor for the quantification of α-feto protein (AFP) using a nanocomposite of manganese(iv) oxide nanorods (MnO₂NRs) and gold nanoparticles (AuNPs) as the immobilisation layer is presented.     

Sensitive electrochemical sensor based on poly(l-glutamic acid)/graphene oxide composite material for simultaneous detection of heavy metal ions

Heavy metal pollution can be toxic to humans and wildlife, thus it is of great significance to develop rapid and sensitive methods to detect heavy metal ions. Here, a novel type of electrochemical sensor for the simultaneous detection of heavy metal ions has been prepared by using poly(l-glutamic acid) (PGA) and graphene oxide (GO) composite materials to modify the glassy carbon electrode (GCE). Due to the good binding properties of poly(l-glutamic acid) (PGA) for the heavy metal ions (such as Cu²⁺, Cd²⁺, and Hg²⁺) as well as good electron conductivity of graphene oxide (GO), the heavy metal ions, Cu²⁺, Cd²⁺, and Hg²⁺ in aqueous solution can be accurately detected by using differential pulse anodic stripping voltammetry method (DPASV). Under the optimized experiment conditions, the modified GCE shows excellent electrochemical performance toward Cu²⁺, Cd²⁺, and Hg²⁺, and the linear range of PG/GCE for Cu²⁺, Cd²⁺, and Hg²⁺ is 0.25–5.5 μM, and the limits of detection (LODs, S/N ≥ 3) Cu²⁺, Cd²⁺, and Hg²⁺ are estimated to be 0.024 μM, 0.015 μM and 0.032 μM, respectively. Moreover, the modified GCE is successfully applied to the determination of Cu²⁺, Cd²⁺, and Hg²⁺ in real samples. All obtained results show that the modified electrode not only has the advantages of simple preparation, high sensitivity, and good stability, but also can be applied in the field of heavy metal ion detection.

A novel electrochemical sensor with high stability and good reproducibility for the simultaneous detection of heavy metal ions was prepared by using PGA/GO to modify the GCE, showing high sensitivity of superior to most of the reported values.     

Fluorescent sensing platform based on green luminescence carbon dots and AuNPs for clenbuterol detection in pork liver

In this paper, water-soluble green fluorescent carbon dots (G-CDs) were prepared using p-phenylenediamine and glutathione (GSH) as the precursors. The G-CDs exhibit excellent optical properties, and the maximum emission wavelength is located at 522 nm (under 410 nm excitation), which greatly overlaps with the absorption spectrum of AuNPs. Consequently, an effective “off–on” fluorescent sensing platform involved in G-CDs and AuNPs for detection of clenbuterol (CLB) was constructed. The fluorescence of G-CDs was strongly quenched by AuNPs due to the inner filter effect (IFE). As CLB was introduced, the quenched fluorescence intensity was recovered due to the specific interaction between the AuNPs and CLB. The recovered fluorescence intensity is linear to CLB concentration in the range of 13–270 ng mL⁻¹ with a low detection limit of 3.75 ng mL⁻¹. The prepared sensor has been successfully applied for CLB detection in pork liver and could be utilized in food analysis.

Carbon dots (G-CDs) with bright green fluorescence are synthesized by hydrothermal treatment of p-phenylenediamine and glutathione. Employing the G-CDs and AuNPs as sensing platform, a simple fluorescence sensor to detect clenbuterol was established.     

Experimental and theoretical approaches for the selective detection of thymine in real samples using gold nanoparticles as a biochemical sensor

We report a simple, selective and cost effective method for the qualitative and quantitative determination of thymine in a DNA standard and urine samples using gold nanoparticles (AuNPs) as a label-free colorimetric biochemical sensor. The mechanism for the detection of thymine is demonstrated via the color change of the AuNPs from pink to blue, followed by the shift of the localized surface plasmon resonance (LSPR) absorption band to a higher wavelength with the introduction of an analyte. The selective detection of thymine was experimentally verified by performing a control experiment with nucleobases, other biomolecules, metal ions and anions. In addition, the computation density functional theory (DFT) and time dependent density functional theory (TD-DFT) using the Gaussian (C.01) program highlighted that the electrostatic potential behavior of the thymine molecule facilitated a non-covalent interaction toward gold for the selective detection of analytes, and the computation was also used to calculate a UV-Vis absorption band as well. The calculated absorption band of the AuNPs with thymine, obtained using TD-DFT, was found to be very close to the experimental data. The omnicapped truncated tetrahedral (ν₃-tetrahedral) Au₂₀ cluster structure was considered as the model for the AuNP optimization. The linear range obtained for the quantitative determination of thymine was found to be 10–1200 ng mL⁻¹ with a limit of detection of 3 ng mL⁻¹. The advantages of using the AuNPs as a biochemical sensor are that they provide a facile and low cost method and are selective for the qualitative and quantitative determination of thymine in a DNA standard and in urine samples in comparison to chromatographic and electrochemical methods.

We report a simple, selective and cost effective method for the qualitative and quantitative determination of thymine in a DNA standard and in urine samples using gold nanoparticles (AuNPs) as a label-free colorimetric biochemical sensor.     

A novel ultrasensitive surface plasmon resonance-based nanosensor for nitrite detection

Nitrite is a common food additive, however, its reduction product, nitrosamine, is a strong carcinogen, and hence the ultra-sensitive detection of nitrite is an effective means to prevent related cancers. In this study, different sized gold nanoparticles (AuNPs) were modified with P-aminothiophenol (ATP) and naphthylethylenediamine (NED). In the presence of nitrite, satellite-like AuNPs aggregates formed via the diazotization coupling reaction and the color of the system was changed by the functionalized AuNPs aggregates. The carcinogenic nitrite content could be detected by colorimetry according to the change in the system color. The linear concentration range of sodium nitrite was 0–1.0 μg mL⁻¹ and the detection limit was determined to be 3.0 ng mL⁻¹. Compared with the traditional method, this method has the advantages of high sensitivity, low detection limit, good selectivity and can significantly lower the naked-eye detection limit to 3.0 ng mL⁻¹. In addition, this method is suitable for the determination of nitrite in various foods. We think this novel designed highly sensitive nitrate nanosensor holds great market potential.

A satellite-like AuNP aggregate-based nitrite detection nanosensor was designed via diazotization coupling reaction and can significantly lower the naked-eye detection limit to 3.0 ng mL⁻¹. This nanosensor has important applications in food detection and cancer prevention.     

Synthesis of MoS2 nanosheets for mercury speciation analysis by HPLC-UV-HG-AFS

Mercury species have aroused wide concern in the past several decades due to their high toxicity. However, it is still difficult to detect ultra-trace mercury species due to their biochemical transformation in complex samples. To establish a simpler and more sensitive method for pre-concentration and determination of trace mercury species, molybdenum disulfide (MoS₂) nanosheets with sulfur-rich characteristics and enlarged interlayer spacing were prepared by a hydrothermal method coupled with a sonication-assisted liquid exfoliation method and acted as solid-phase extraction adsorbent. The nano-MoS₂ had high adsorption capacity, fast adsorption rate and excellent selectivity towards mercury ions (Hg²⁺), methyl mercury (MeHg⁺) and ethyl mercury (EtHg⁺) in a wide pH range and complex matrices. And it could be easily regenerated by 4 mol L⁻¹ HCl and reused several times. After optimizing HPLC-UV-HG-AFS conditions, a great linearity (1.0–10.0 μg L⁻¹, R² = 0.999 for Hg²⁺, MeHg⁺ and EtHg⁺), lower detection limits (0.017, 0.037 and 0.021 ng mL⁻¹ for Hg²⁺, MeHg⁺ and EtHg⁺, respectively), relative standard deviations (<5%) and addition recoveries of the samples within 82.75–113.38% were observed. In summary, trace inorganic and organic mercury species in environmental and biological samples could be selectively enriched by the prepared nano-MoS₂ and efficiently seperated and detected by HPLC-UV-HG-AFS. The present study will help provide a better strategy for environmental monitoring and health assessment of mercury pollutants.

As-synthesized few-layered molybdenum disulfide nanosheets were used as solid-phase extraction absorbent for ultra-trace mercury speciation analysis by HPLC-UV-HG-AFS.     

On-site,rapid and visual method for nanomolar Hg2+ detection based on the thymine–Hg2+–thymine triggered “double” aggregation of Au nanoparticles enhancing the Tyndall effect

This work describes a new nanosensor for the simple, rapid, portable, colorimetric analysis of mercury(ii) (Hg²⁺) ions by combining the sensitive Tyndall effect (TE) of colloidal Au nanoparticles (AuNPs) with specific thymine–Hg²⁺–thymine (T–Hg²⁺–T) coordination chemistry for the first time. For the TE-inspired assay (TEA), in the presence of Hg²⁺ in a sample, the analyte can selectively mediate the hybridization of three types of flexible single-stranded DNAs (ssDNAs) to form stable rigid double-stranded DNAs (dsDNAs) via the T–Hg²⁺–T ligand interaction. Subsequent self-assembly of the dsDNAs with terminal thiol groups on the AuNPs'' surfaces led to their “double” aggregation in addition to the lack of sufficient ssDNAs as the stabilizing molecules in a high-salt solution, resulting in a remarkably enhanced TE signal that positively relied on the Hg²⁺ level. The results demonstrated that such a TEA method enabled rapid naked-eye qualitative analysis of 625 nM Hg²⁺ within 10 min with an inexpensive laser pointer pen as an inexpensive handheld light source to generate the TE response. Making use of a smartphone for portable TE readout could further quantitatively detect the Hg²⁺ ions in a linear concentration range from 156 to 2500 nM with a limit of detection as low as 25 nM. Moreover, the developed equipment-free nanosensor was also used to analyze the Hg²⁺ ions in real samples including tap water, drinking water, and pond water, the obtained recoveries were within the range of 93.68 to 108.71%. To the best of our knowledge, this is the first report of using the AuNPs and functional nucleic acids to design a TE-based biosensor for the analysis of highly toxic heavy metal ions.

A new equipment-free colorimetric nanosensor was initially developed for quantitative point-of-need detection of nanomolar Hg²⁺ ions based on the enhancement in Tyndall effect of Au nanoparticles via their target-triggered “double” aggregation.     

Robust colorimetric detection based on the anti-aggregation of gold nanoparticles for bromide in rice samples

Inorganic bromide (Br⁻) is an important contaminant ion as it can originate from the overuse of illegal methyl bromide as a fumigant in stored rice samples. Herein, we developed a simple and highly sensitive colorimetric sensor for bromide ion detection in rice samples. The sensor is based on the anti-aggregation of gold nanoparticles (AuNPs) by Br⁻ in the presence of Cr³⁺, which made the method more selective than other typical aggregations of nanoparticles. The AuNPs underwent an aggregation process as a result of the coordination of Cr³⁺ and the carboxylate group of a citrate ion stabilized the AuNPs, resulting in a red-to-blue color change. When Br⁻ was pre-mixed with the AuNPs and Cr³⁺ was added, the solution color changed from blue to red with an increase in the Br⁻ concentration. The anti-aggregation process can be detected with the naked eye and monitored using UV-vis spectrophotometry. The linear calibration curve ranged between 0.31 and 3.75 μM Br⁻ with a low LOD and LOQ of 0.04 and 0.13 μM. The recovery was excellent, ranging from 79.9–92.2% with an RSD of less than 4.0%. The good inter-day and intra-day precisions were 2.9–6.4% and 3.1–7.1%, respectively. The developed sensor has proved to provide a robust method for Br⁻ detection in rice samples.

In this work, we developed a AuNP colorimetric sensor for the facile, sensitive and selective detection of bromide ions in rice samples.     

Selective separation of uranyl ions from some lanthanide elements using a promising β-enaminoester ligand by cloud point extraction

For uranyl extraction, a distinctive chelating ligand, namely ethyl 2-amino-6-hydroxy-5-(4-methoxyphenyldiazenyl)-4-phenyl-4H-benzo[f]chromene-3-carboxylate, has been synthesized and characterized using FT-IR, NMR, and ESI-MS. Subsequently, a cloud point extraction (CPE) protocol has been developed for the selective separation of the trace amounts of uranyl ions from some lanthanide ions after being captured by the ligand in the presence of non-ionic surfactant (Triton X-114). The extraction procedure has been optimized based on the concentration of the complexing agent and the non-ionic surfactant, phase separation temperatures, pH, and ionic strength. The developed CPE procedure exhibited a relatively low detection limit of 0.5 ng mL⁻¹ in the linear range from 3 ng mL⁻¹ to 250 ng mL⁻¹. Furthermore, interference studies have been carried out to study the selectivity of our protocol. These studies revealed that the recoveries of uranyl ions were in the range from 96.1% to 99.9% in the presence of some lanthanide ions such as Th⁴⁺, Gd³⁺, and Sm³⁺. It is worth mentioning that the geometry optimization, reactivity, and molecular electrostatic potential maps of the ligand and the proposed UO₂²⁺ complex were acquired via DFT calculations to study their stabilities based on the geometry and binding affinity. The theoretical data confirmed the octahedral geometry of the UO₂²⁺ complex with the lowest energy and excellent stability. The robustness of the proposed methodology was evaluated by the detection of uranyl ions in different environmental samples and synthetic mixtures.

For uranyl extraction, a distinctive chelating ligand, namely ethyl 2-amino-6-hydroxy-5-(4-methoxyphenyldiazenyl)-4-phenyl-4H-benzo[f]chromene-3-carboxylate, has been synthesized and characterized using FT-IR, NMR, and ESI-MS.     

Ultrathin quasi-hexagonal gold nanostructures for sensing arsenic in tap water

Monodispersed colloidal gold nanoparticles (AuNPs) were synthesized by an easy, cost-effective, and eco-friendly method. The AuNPs were mostly quasi-hexagonal in shape with sizes ranging from 15 to 18 nm. A screen-printed electrode modified with AuNPs (AuNPs/SPE) was used as an electrochemical sensor for the detection of As(iii) in water samples. The mechanistic details for the detection of As(iii) were investigated and an electrochemical reaction mechanism was proposed. Under the optimal experimental conditions, the sensor was highly sensitive to As(iii), with a limit of detection of 0.11 μg L⁻¹ (1.51 nM), which is well below the regulatory limit of 10 μg L⁻¹ established by the United States Environmental Protection Agency and the World Health Organization. The sensor responses were highly stable, reproducible, and linear over the As(iii) concentration range of 0.075 to 30 μg L⁻¹. The presence of co-existing heavy metal cations such as lead, copper, and mercury did not interfere with the sensor response to As(iii). Furthermore, the voltammogram peaks for As(iii), lead, copper, and mercury were sufficiently separate for their potential simultaneous measurement, and at very harsh acidic pH it may be possible to detect As(v). The AuNPs/SPE could detect As(iii) in tap water samples at near-neutral pH, presenting potential possibilities for real-time, practical applications.

Monodispersed colloidal gold nanoparticles (AuNPs) were synthesized by an easy, cost-effective, and eco-friendly method for electrochemical detection of As(iii).     

Tailoring the dimensionality of carbon nanostructures as highly electrochemical supports for detection of carcinoembryonic antigens

Partially- and fully-unzipped nitrogen-doped carbon nanotubes (NCNTs) were prepared by unzipping pristine NCNTs and three carbon nanostructures were applied to support Au nanoparticles (AuNPs) to form nanocomposites (Au/NCNTs, Au/PU-NCNTs, and Au/FU-NCNTs). The electrochemical behavior and the electrocatalytic activities of the nanocomposite-modified electrodes were examined. The oxygen functional groups, doped N content, and AuNP loaded concentrations are dependent on the unzipping-degree and then affect the electrochemical response and electrocatalytic performance of the electrodes. Besides, the three nanocomposites were also used for the immobilization of carcinoembryonic antigen (CEA) aptamer strands and applied for the detection of CEA. The Au/FU-NCNTs possess the optimal electrocatalytic activity and biosensing performance for the biomolecules and CEA, which is attributed to the maximum loaded AuNPs, the largest specific surface areas and the most active sites. The Au/FU-NCNT-based electrochemical aptasensor exhibits high sensitivity with a low detection limit of 6.84 pg mL⁻¹ within a broad linear range of CEA concentration from 0.01 to 10 ng mL⁻¹. All of these results indicate that the Au/FU-NCNTs may be a potential support for construction of aptasensors with high electrochemical effect and can be employed in the fields of biosensing or biomedical diagnosis.

Nitrogen-doped carbon nanotube derivatives were chosen to support Au nanoparticles to form nanocomposites (Au/NCNTs, Au/PU-NCNTs and Au/FU-NCNTs). The Au/FU-NCNTs possess the optimal electrocatalytic activity and biosensing performance for carcinoembryonic antigen (CEA).     

Effective screen-printed potentiometric devices modified with carbon nanotubes for the detection of chlorogenic acid: application to food quality monitoring

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection. The screen-printed platforms were modified with multi-walled carbon nanotubes (MWCNTs) to work as a lipophilic solid-contact transducer. The sensing-membrane was plasticized with a suitable solvent mediator and incorporating [Ni^II(bathophenanthroline)₃][CGA]₂ complex as a sensory material. In a 30 mM phosphate solution (buffer, pH 6), the sensor revealed a Nernstian-response towards CGA ions with a slope of −55.1 ± 1.1 (r² = 0.9997) over the linear range 1.0 × 10⁻⁷ to 1.0 × 10⁻³ (0.035–354.31 μg mL⁻¹) with a detection limit 7.0 × 10⁻⁸ M (24.8 ng mL⁻¹). It revealed a stable potentiometric response with excellent reproducibility and enhanced selectivity over several common ions. Short-term potential stability and the interfacial sensor capacitance was estimated using both electrochemical-impedance spectroscopy (EIS) and chronopotentiometry techniques. The presented electrochemical platform revealed the merits of design simplicity, ease of miniaturization, good potential-stability, and cost-effectiveness. It is successfully applied to CGA determination in different coffee beans extracts and juice samples. The data obtained were compared with those obtained by liquid chromatography reference method (HPLC).

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection.     

A dual colorimetric probe for rapid environmental monitoring of Hg2+ and As3+ using gold nanoparticles functionalized with d-penicillamine

A highly sensitive and selective colorimetric assay for the dual detection of Hg²⁺ and As³⁺ using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed. When Hg²⁺ and As³⁺ ions coordinate with AuNP-bound DPLs, the interparticle distance decreases, inducing aggregation; this results in a significant color change from wine red to dark midnight blue. The Hg4f and As3d signals in the X-ray photoelectron spectra of Hg²⁺ (As³⁺)-DPL-AuNPs presented binding energies indicative of Hg²⁺–N(O) and As³⁺–N(O) bonds, and the molecular fragment observed in time-of-flight secondary ion mass spectra confirmed that Hg²⁺ and As³⁺ coordinated with two oxygen and two nitrogen atoms in DPL. The detection of Hg²⁺ and As³⁺ can be accomplished by observing the color change with the naked eye or by photometric methods, and this was optimized to provide optimal probe sensitivity. The assay method can be applied for environmental monitoring by first selectively quantifying Hg²⁺ in water samples at pH 6, then estimating the As³⁺ concentration at pH 4.5. The efficiency of the DPL-AuNP probe was evaluated for the sequential quantification of Hg²⁺ and As³⁺ in tap, pond, waste, and river water samples, and absorbance ratios (A₇₃₀/A₅₂₅) were correlated with Hg²⁺ and As³⁺ concentrations in the linear range of 0–1.4 μM. The limits of detection in water samples were found to be 0.5 and 0.7 nM for Hg²⁺ and As³⁺, respectively. This novel probe can be utilized for the dual determination of Hg²⁺ and As³⁺, even in the presence of interfering substances in environmental samples.

A highly sensitive and selective colorimetric assay for the dual detection of Hg²⁺ and As³⁺ using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed.     

Functionalization of silver nanoparticles with mPEGylated luteolin for selective visual detection of Hg2+ in water sample

A novel colorimetric sensor based on mPEGylated luteolin-functionalized silver nanoparticles (mPEGylated luteolin-AgNPs) in an aqueous solution was prepared. The mPEGylated luteolin-AgNP solution was utilized to detect Hg²⁺ with high sensitivity and selectivity in the presence of other metal cations including Na⁺, K⁺, Mg²⁺, Zn²⁺, Ni²⁺, Mn²⁺, Ba²⁺, Pb²⁺, Sr²⁺, Ca²⁺, Cd²⁺, Al³⁺ and Cu²⁺. The solution could be induced to aggregate, and a color change from yellow-brown to colorless was observed in the presence of Hg²⁺. Meanwhile, the sensor was successfully used to detect Hg²⁺ in tap water with satisfactory recovery ranges using the standard addition method.

A novel colorimetric sensor for selective detection of Hg²⁺ based on mPEGylated luteolin functionalized silver nanoparticles was prepared.     

Integration detection of mercury(ii) and GSH with a fluorescent “on-off-on” switch sensor based on nitrogen,sulfur co-doped carbon dots

Using aurine and citric acid as precursors, we have synthesized stable blue-fluorescent nitrogen and sulfur co-doped carbon dots (NS-CDs), with a high quantum yield of up to 68.94% via a thermal lysis method. The fluorescent NS-CDs were employed as a sensitive sensor for the integration detection of Hg²⁺ and glutathione (GSH). This was attributed to Hg²⁺ effectively quenching the fluorescence of the NS-CDs by static quenching, and then GSH was able to recover the fluorescence owing to the stronger binding between Hg²⁺ and the sulfhydryl of GSH. Based on the “on-off-on” tactic, the detection limits of Hg²⁺ ions and GSH were 50 nM and 67 nM respectively. The fluorescence sensor was successfully applied to detect Hg²⁺ ions and GSH in actual samples (tap water and fetal bovine serum). Furthermore, we have proved that the sensor had good reversibility. Overall, our NS-CDs can serve as effective sensors for environmental and biological analysis in the future.

NS-CDs are employed as a sensitive sensor for the integration detection of Hg²⁺ and GSH. Hg²⁺ effectively quenching the fluorescence by static quenching. GSH is able to recover the fluorescence owing to the stronger binding between Hg²⁺ and GSH.     

Sensitive and selective detection of the highly toxic pesticide carbofuran in vegetable samples by a molecularly imprinted electrochemical sensor with signal enhancement by AuNPs

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity. AuNPs were used as the electron wire for signal amplification, and molecularly imprinted polymer was used as the recognition element. The preparation process of the modified electrode was optimized, and the electrode was characterized using scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry. The results proved that the prepared sensor can selectively detect carbofuran and the AuNPs can increase its sensitivity. The method validation included the systematic evaluation of the linearity, sensitivity, selectivity, reproducibility and stability. The optimized sensor showed a wide linear response to carbofuran in the range from 5.0 × 10⁻⁸ to 4.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.4 × 10⁻⁸ mol L⁻¹. The sensor also exhibited a high selectivity to carbofuran. The real sample analysis for vegetable samples suggested its potential application in the analysis of vegetable samples.

An imprinted electrochemical sensor was constructed for the detection of carbofuran with high sensitivity and selectivity.     

Rapid electrochemical quantification of trace Hg2+ using a hairpin DNA probe and quantum dot modified screen-printed gold electrodes

Rapid, simple, sensitive and specific approaches for mercury(ii) (Hg²⁺) detection are essential for toxicology assessment, environmental protection, food analysis and human health. In this study, a ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quaternary Zn–Ag–In–S quantum dot (QD) on screen-printed gold electrodes (SPGE), referred to as the HP-QDs-SPGE electrochemical biosensor in this study, was developed for Hg²⁺ detection. Based on the “turn-off” reaction of a hairpin DNA probe binding with a mismatched target and Hg²⁺ through the formation of T–Hg²⁺–T coordination, the HP-QDs-SPGE electrochemical biosensor can rapidly quantify trace Hg²⁺ with high ultrasensitivity, specificity, repeatability and reproducibility. The conformational change of the hairpin DNA probe caused a significant decrease in electrochemical intensity, which could be used for the quantification of Hg²⁺. The linear dynamic range and high sensitivity of the HP-QDs-SPGE electrochemical biosensor for the detection of Hg²⁺ was studied in vitro, with a broad linear dynamic range of 10 pM to 1 μM and detection limits of 0.11 pM. In particular, this HP-QDs-SPGE electrochemical biosensor showed excellent selectivity toward Hg²⁺ ions in the presence of other metal ions. More importantly, this biosensor has been successfully used to detect Hg²⁺ in deionized water, tap water, groundwater and urine samples with good recovery rate and small relative standard deviations. In summary, the developed HP-QDs-SPGE electrochemical biosensor exhibited promising potential for further applications in on-site analysis.

A ratiometric hairpin DNA probe based electrochemical biosensor, which relies on hairpin DNA probes conjugated with water-soluble and carboxyl functionalized quantum dot on screen-printed gold electrodes, was developed for Hg²⁺ detection.     

Thiolated poly(aspartic acid)-functionalized two-dimensional MoS2, chitosan and bismuth film as a sensor platform for cadmium ion detection

In this work, a sensitive electrochemical platform for determination of cadmium ions (Cd²⁺) is obtained using thiolated poly(aspartic acid) (TPA)-functionalized MoS₂ as a sensor platform by differential pulse anodic stripping voltammetry (DPASV). The performance of the TPA–MoS₂-modified sensor is systemically studied. It demonstrates that the TPA–MoS₂ nanocomposite modified sensor exhibits superior analytical performance for Cd²⁺ over a linear range from 0.5 μg L⁻¹ to 50 μg L⁻¹, with a detection limit of 0.17 μg L⁻¹. Chitosan is able to form a continuous coating film on the surface of the GC electrode. The good sensing performance of the TPA–MoS₂-modified sensor may be attributed to the following factors: the large surface area of MoS₂ (603 m² g⁻¹), and the abundant thiol groups of TPA. Thus, the TPA–MoS₂-modified sensor proves to be a reliable and environmentally friendly tool for the effective monitoring of Cd²⁺ existing in aquacultural environments.

In this work, a sensitive electrochemical platform for determination of cadmium ions (Cd²⁺) is obtained using thiolated poly(aspartic acid) (TPA)-functionalized MoS₂ as a sensor platform by differential pulse anodic stripping voltammetry (DPASV).     

Two novel colorimetric fluorescent probes: Hg2+ and Al3+ in the visual colorimetric recognition environment

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg²⁺ and Al³⁺, respectively. The two probes were characterized by FTIR, ¹H NMR, ¹³C NMR and HRMS, and their optical properties were detected by UV and FL. Test results showed the probes'' detection of Hg²⁺ and Al³⁺ compared to other metal ions (Ag⁺, Co²⁺, Cd²⁺, Mg²⁺, Cu²⁺, Ni²⁺, Ba²⁺, Pb²⁺, Cr³⁺, Al³⁺, Zn²⁺, Hg²⁺, K⁺, Ga²⁺ and Fe³⁺), respectively. Besides, the detection limits were determined to be 1.61 × 10⁻⁸ M and 1.15 × 10⁻⁸ M through the standard curve plot, respectively. The photoelectron transfer (PET) mechanism was guessed by the Job''s plot and the infrared titration. Corresponding orbital electron distribution and molecular geometry configurations of the compounds were predicted by density functional theory (DFT). In addition, the prepared test paper changed from white to pink when the target ion was detected. The color changed from colorless to pink in a solution having a concentration of 10⁻⁵ M.

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg²⁺ and Al³⁺, respectively.     

Selective and sensitive spectrofluorimetric quantification of velpatasvir in presence of sofosbuvir. Application to their co-formulated tablet

A new sensitive, rapid and simple spectrofluorimetric method was utilized for the assessment of velpatasvir (VPS) in its bulk form as well as in its combined tablet with sofosbovir (SFV). The technique relies on measuring the native fluorescence of VPS in methanol at 385 nm and 400 nm after excitation at 295 nm. The fluorescence–concentration plots were rectilinear through the range of 2.0–20.0 ng mL⁻¹ at both emission maxima with lower detection limits of 0.146 ng mL⁻¹ and 0.378 ng mL⁻¹, and lower quantification limits of 0.444 ng mL⁻¹ and 1.147 ng mL⁻¹ at 385 nm and 400 nm, respectively. The proposed method was appropriately used for the analysis of VPS in its commercial tablet formulation and the results were in good agreement with those achieved with the applied comparison method.

A new sensitive, rapid and simple spectrofluorimetric method was utilized for the assessment of velpatasvir (VPS) in its bulk form as well as in its combined tablet with sofosbovir (SFV).