Post-synthetic modification of graphene quantum dots bestows enhanced biosensing and antibiofilm ability: efficiency facet

Graphene quantum dots (GQDs) are a luminescent class of carbon nanomaterials with a graphene-like core structure, possessing quantum confinement and edge effects. They have gained importance in the biological world due to their inherent biocompatibility, good water dispersibility, excellent fluorescence and photostability. The improved properties of GQDs require the logical enactment of functional groups, which can be easily attained through post-synthetic non-covalent routes of modification. In this regard, the present work has for the first time employed a simple one-pot post-modification method utilizing the salt of amino caproic acid, an FDA approved reagent. The adsorption of the modifier on GQDs with varying weight ratios is characterized through DLS, zeta potential, Raman, absorption and fluorescence spectroscopy. A decrease of 20% in the fluorescence intensity with an increase in the modifier ratio from 1 to 1000 and an increased DLS size as well as zeta potential demonstrate the efficient modification as well as higher stability of the modified GQDs. The modified GQDs with a high weight ratio (1 : 100) of the modifier showed superior ability to sense dopamine, a neurotransmitter, as well as competent biofilm degradation ability. The modified GQDs could sense more efficiently than pristine GQDs, with a sensitivity as low as 0.06 μM (limit of detection) and 90% selectivity in the presence of other neurotransmitters. The linear relationship showed a decrease in the fluorescence intensity with increasing dopamine concentration from 0.0625 μM to 50 μM. Furthermore, the efficiency of the modified GQDs was also assessed in terms of their antibiofilm effect against Staphylococcus aureus. The unmodified GQDs showed only 10% disruption of the adhered bacterial colonies, while the modified GQDs (1 : 100) showed significantly more than 60% disruption of the biofilm, presenting the competency of the modified GQDs. The unique modifications of GQDs have thus proven to be an effective method for the proficient utilization of zero-dimensional carbon nanomaterials for biosensing, bioimaging, antibacterial and anti-biofilm applications.

The present work highlights a novel post-synthetic modification route for graphene quantum dots, which was found to be efficient for both the biosensing of dopamine as well as Staphylococcus aureus biofilm degradation.     

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.     

Photostimulated control of luminescence quantum yield for colloidal Ag2S/2-MPA quantum dots

In this paper, we present the results on photoinduced formation of colloidal Ag₂S quantum dots with sizes of 1.5–3 nm passivated by 2-mercaptopropionic acid (Ag₂S/2-MPA) in the presence of ethylene glycol. The synthetized colloidal Ag₂S/2-MPA QDs have NIR recombination luminescence with its maximum near 800 nm. The control of absorption and luminescence properties of the QDs is achieved by photoactivation. It is shown that photoexposure of colloidal solution of Ag₂S/2-MPA QDs leads to an increase in the QD size and monodispersity along side with the growth of the luminescence quantum yield from 1% to 7.9%. Enhancement of the luminescence quantum yield is accompanied by an increase in the average luminescence lifetime up to 190 ns, which is due to the blocking of the nonradiative recombination channel with the radiative recombination rate being (3–5.5) × 10⁵ s⁻¹. It is shown that the purification of the Ag₂S/2-MPA solution by a dialysis membrane from regenerated cellulose leads to an increase in the sample monodispersity, as well as stops the photoinduced growth of QDs, and also reduces the degradation of their photoluminescence.

In this paper, we present the results on photoinduced formation of colloidal Ag₂S quantum dots with sizes of 1.5–3 nm passivated by 2-mercaptopropionic acid (Ag₂S/2-MPA) in the presence of ethylene glycol.     

The structural and luminescence properties of plexcitonic structures based on Ag2S/l-Cys quantum dots and Au nanorods

A technique of obtaining plexitonic structures based on Ag₂S quantum dots passivated with l-cysteine (Ag₂S/l-Cys QDs) in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs) with controlled luminescence properties has been developed. The structural and luminescence properties of Ag₂S/l-Cys QDs with Au/CTAB NRs are studied. The effect of plasmonic Au/CTAB NRs on IR trap state luminescence (750 nm) is considered. It has been found that the direct interaction between the components of the plexcitonic nanostructure leads to a significant luminescence quenching of Ag₂S/l-Cys QDs, with the luminescence lifetime being constant. This is the evidence for photoinduced charge transfer. The spatial separation of the components of plexcitonic nanostructures due to the introduction of a polymer – poly(diallyldimethylammonium chloride) (polyDADMAC) provides a means to change their mutual arrangement and achieve an increase in the IR trap state luminescence intensity and a decrease in the luminescence lifetime from 7.2 ns to 4.5 ns. With weak plexcitonic coupling in the nanostructures [Ag₂S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs], the possibility of increasing the quantum yield of trap state luminescence for Ag₂S QDs due to the Purcell effect has been demonstrated. In the case of formation [Ag₂S QD/l-Cys]/[polyDADMAC]/[Au/CTAB NRs] a transformation of shallow trap state structure was established using the thermostimulated luminescence method.

A technique of obtaining plexitonic structures based on Ag₂S quantum dots passivated with l-cysteine (Ag₂S/l-Cys QDs) in the presence of Au nanorods passivated with cetyltrimethylammonium bromide molecules (Au/CTAB NRs) with controlled luminescence was developed.     

Correction: The structural and luminescence properties of plexcitonic structures based on Ag2S/l-Cys quantum dots and Au nanorods

Correction for ‘The structural and luminescence properties of plexcitonic structures based on Ag₂S/l-Cys quantum dots and Au nanorods’ by Irina G. Grevtseva et al., RSC Adv., 2022, 12, 6525–6532, DOI: 10.1039/D1RA08806H.

The authors regret the omission of a funding acknowledgement in the original article. This acknowledgement is given below.This study was supported by the Ministry of Science and Higher Education of the Russian Federation under Agreement N 075-15-2021-1351 as part of the structural analysis of colloidal Ag₂S/l-Cys QDs and Au NRs.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Cancer antigen 125 assessment using carbon quantum dots for optical biosensing for the early diagnosis of ovarian cancer

Fluorometric quantification of biological molecules is a key feature used in many biosensing studies. Fluorescence resonance energy transfer (FRET) using highly fluorescent quantum dots offers highly sensitive detection of the in-proximity wide variety of analyst molecules. In this contribution, we report the use of carbon quantum dots (CDs) for the ultrasensitive optical biosensing of cancer antigen 125 (CA-125) in the early malignant stage. This approach is based on monitoring the quenching of CDs luminescence at 535 nm by CA-125 after excitation at 425 nm and pH 10. The calibration of this method was performed in the concentration range of CA-125 from 0.01 to 129 U ml⁻¹ (R² = 0.99) with a detection limit of 0.66 U ml⁻¹, which matches remarkably with the standard chemiluminometric method in control and real patient samples. The sensing mechanism for cancer antigen 125 assessment was discussed on the basis of fluorescence quenching of CDs and time-resolved photoluminescence spectroscopy. The current method is easy, sensitive, cost-effective and provides a wide range of validity, which helps in overcoming the limitations of high cost and time consumption exhibited by many other traditional clinical assays for CA-125 quantification.

Fluorometric quantification of biological molecules is a key feature used in many biosensing studies.     

量子点技术快速检测HCV核心抗原的研究

目的采用量子点和磁微粒技术,建立丙型肝炎病毒（HCV）核心抗原的检测体系,并对其临床应用进行初步探讨。方法以碳二亚胺交联法活化量子点及磁微粒,以针对HCV核心抗原不同抗原决定簇的抗体与之连接,和ELISA及FQ-PCR法同时检测临床标本68例,并对结果进行比较。结果量子点磁微粒体系检测阳性11例、阴性57例;ELISA方法检测阳性8例、阴性60例;FQ-PCR检测阳性11例、阴性57例。量子点磁微粒体系检测HCV核心抗原与PCR方法相比,特异度为96．5％,灵敏度为81．8％;检测时间在40min内,灵敏度及特异度无显著性差异,且与HAV-IgM、HBV表面抗原阳性标本无交叉反应。结论量子点磁微粒体系检测HCV核心抗原与ELIsA方法相比有较好的灵敏度与特异性,检测时间大为缩短,以本体系快速检测目标抗原是可行的。     

A novel quartz-crystal microbalance humidity sensor based on solution-processible indium oxide quantum dots

Having a large surface area, like the quantum confinement effect also caused by the nano-level size of quantum dots (QDs), creates fantastic potential for humidity sensing. A high concentration of surface adsorption sites initiates an increased response. Porosity between QDs allows fast water vapor penetration and outflow. Here, a quartz-crystal microbalance (QCM) humidity sensor was prepared using indium oxide (In₂O₃) QDs, synthesized via a solvothermal method. After the In₂O₃ QDs were directly spin-coated onto the QCM, an annealing process removed organic long chains and exposed more moisture adsorption sites on the surfaces of the QDs. The annealed QCM humidity sensor exhibited high sensitivity (56.3 Hz per %RH at 86.3% RH), with a fast response/recovery time (14 s/16 s). Long carbon chains were broken down, and hydrogen-bonded hydroxyl groups were chemisorbed to the QDs. The chemical reaction was reduced by these chemisorbed hydrogen-bonded hydroxyl groups. Mass change was mostly caused by fast multilayer physisorption. Thus, the transducer can effectively and precisely monitor the moisture from a person''s breath. In₂O₃ QD-modified QCM sensors demonstrate promising humidity-sensing applications in daily life.

A high-performance QCM humidity sensor was prepared based on In₂O₃ QDs with a high specific surface area.     

Ultra-small aqueous glutathione-capped Ag–In–Se quantum dots: luminescence and vibrational properties

We introduce a direct aqueous synthesis of luminescent 2–3 nm Ag–In–Se (AISe) quantum dots (QDs) capped by glutathione (GSH) complexes, where sodium selenosulfate Na₂SeSO₃ is used as a stable Se²⁻ precursor. A series of size-selected AISe QDs with distinctly different positions of absorption and PL bands can be separated from the original QD ensembles by using anti-solvent-induced size-selective precipitation. The AISe–GSH QDs emit broadband PL with the band maximum varying from 1.65 eV (750 nm) to 1.90 eV (650 nm) depending on the average QD size and composition. The PL quantum yield varies strongly with basic synthesis parameters (ratios of constituents, Zn addition, duration of thermal treatment, etc.) reaching 4% for “core” AISe and 12% for “core/shell” AISe/ZnS QDs. The shape and position of PL bands is interpreted in terms of the model of radiative recombination of a self-trapped exciton. The AISe–GSH QDs reveal phonon Raman spectra characteristic for small and Ag-deficient tetragonal Ag–In–Se QDs. The ability of ultra-small AISe QDs to support such “bulk-like” vibrations can be used for future deeper insights into structural and optical properties of this relatively new sort of QDs.

A direct aqueous synthesis, composition- and size-dependent absorption, photoluminescence, and vibrational properties of ultra-small glutathione-capped Ag-deficient Ag–In–Se quantum dots are reported.     

An eco-friendly imprinted polymer based on graphene quantum dots for fluorescent detection of p-nitroaniline

An eco-friendly fluorescent molecularly imprinted polymer anchored on the surface of graphene quantum dots (GQDs@MIP) was developed with an efficient sol–gel polymerization for highly sensitive and selective determination of p-nitroaniline (p-NA). The GQDs@MIP was characterized in detail by Fourier-transform infrared, fluorescence spectrometer, scanning electron microscope, transmission electron microscope and ultraviolet spectrophotometer. The results showed that the imprinted layer was successfully grafted on the surface of the GQDs. The fluorescence of the GQDs@MIP is efficiently quenched when p-NA recombines with the imprinting sites based on the photo-induced electron transfer fluorescence quenching mechanism. A good linear relationship was obtained between the fluorescence quenching efficiency of the GQDs@MIP and the concentration of p-NA in the range of 0–15.0 μM with a correlation coefficient of 0.99. The practicability of the proposed method in real samples was successfully evaluated through monitoring p-NA in water and fish samples with satisfactory recovery. The developed method provides a feasible and eco-friendly strategy to fabricate MIPs anchored on GQDs with good fluorescence properties for sensitive detection of organic pollutants in complex samples.

An eco-friendly fluorescent molecularly imprinted polymer anchored on the surface of graphene quantum dots (GQDs@MIP) was developed with an efficient sol–gel polymerization for highly sensitive and selective determination of p-nitroaniline (p-NA).     

Ethylenediamine mediated luminescence enhancement of pollutant derivatized carbon quantum dots for intracellular trinitrotoluene detection: soot to shine

Vehicle-generated toxic pollutants are composed of gaseous smoke and particulate byproducts accumulated as a black substance at its exhaust. This particulate matter (soot) is utilized for the green synthesis of highly stable, non-toxic, environment friendly, carbon quantum dots (CQD). The CQDs are synthesized via the simple hydrothermal route in the absence (C1) and presence (C2) of oxidants. The as-synthesized CQDs are amine functionalized using ethylenediamine. The amine functionalized CQDs (C1N and C2N) are explored for trinitrotoluene detection. From transmission electron microscopy, the average size of C1 and C2 was found to be about 4.2 nm and 5.6 nm respectively. The incorporation of amine groups lead to an increase in quantum yields from 5.63% to 12.7% for C1 and from 3.25% to 8.48% for C2 QDs. A limit of detection (LOD) of 13 ppb was displayed by C1N while the LODs of 11 ppb and 4.97 ppb were delivered by C2N at λ_ex 370 nm and λ_ex 420 nm respectively. The Stern–Volmer constant for C1N is 2.02 × 10⁶ M⁻¹ while for C2N at λ_ex 370 nm and λ_ex 420 nm is 0.38 × 10⁶ M⁻¹ and 0.48 × 10⁶ M⁻¹ respectively. Furthermore, C1N presents high selectivity for TNT compared to C2N. Owing to their higher luminescence, C1N particles are successfully demonstrated for their applicability in intracellular TNT detection.

Vehicle-generated toxic pollutants are composed of gaseous smoke and particulate byproducts accumulated as a black substance at its exhaust.     

Colorimetric determination of ascorbic acid based on carbon quantum dots as peroxidase mimetic enzyme

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm. Interestingly, the ox-TMB could be further reduced by ascorbic acid (AA) leading to fading of the blue color and an absorbance decrease. Thus, a convenient and sensitive colorimetric method for detection of AA using CQDs as peroxidase mimics was established. Several factors, such as acidity, temperature, incubating time, and TMB concentration, which might influence the response of the analysis signal, were optimized. The results showed that the decrease of absorbance (ΔA) was in good linear agreement with AA concentration in the range of 1.0–105 μM, with a low detection limit of 0.14 μM. The feasibility of this method was also investigated in commercial beverages with the 94.3–110.0% recovery.

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm.     

Effect of co-sensitization of InSb quantum dots on enhancing the photoconversion efficiency of CdS based quantum dot sensitized solar cells

The effect of co-sensitization of CdS and InSb Quantum Dots (QDs) on the enhancement of efficiency of Quantum Dots Sensitized Solar Cells (QDSSCs) has been investigated. InSb is synthesized by a facile solvothermal method using indium metal particles and antimony trichloride as precursors. From TEM images the average particle size of InSb was found to be less than 25 nm. The I–V data showed photoconversion efficiency (PCE) of 0.8% using InSb QDs as a sensitizer layer for QDSSC. However, co-sensitization of InSb QDs and CdS QDs on the TiO₂ photoanode in QDSSCs showed an enhanced PCE of 4.94% compared to that of CdS sensitized solar cells (3.52%). The InSb QD layer broadens the light absorption range with reduced spectral overlap causing an improvement in light harvesting along with suppression of surface defects which reduced the recombination losses. As a result, co-sensitized TiO₂/CdS/InSb QDSSC exhibits a greatly improved PCE of 4.94%, which is 40% higher than that of TiO₂/CdS (3.52%) based QDSSCs due to improved light absorption with low recombination losses.

InSb co-sensitized QDSSCs showed relatively higher efficiency (4.94%) than CdS based QDSSCs (3.52%) due to improved light absorption with low recombination losses.     

Development of a fluorescent immunochromatographic assay based on quantum dots for the detection of fleroxacin

Fleroxacin (FLE) is a broad-spectrum fluoroquinolone antibiotic widely used in animal husbandry, veterinary medicine and aquaculture. Eating animal-derived foods with FLE residues can cause allergies, poisoning or drug resistance. The water-soluble QDs (CdSe/ZnS) and anti-FLE monoclonal antibody (mAb) were used to prepare a fluorescent probe by the method of N-(3-dimethylaminopropyl)-N′-ethylcarbodimide hydrochloride (EDC) activation. The fluorescent probe was characterized by dynamic light scattering (DLS). The better bioactivity and stability of the fluorescent probe was obtained under the pH value of 8.0, the molecule molar ratio of EDC (1 : 2000) and anti-FLE monoclonal antibodies (1 : 10). The control line (C line) and test line (T line) of a nitrocellulose (NC) filter membrane were sprayed with SPA (0.05 mg mL⁻¹) and FLE-OVA (1.4 mg mL⁻¹) solutions with optimal concentration, respectively. A novel method of fluorescent immunochromatographic assay based on quantum dots (QDs-ICA) in this work exhibited good accuracy, reproductivity and excellent specificity under the optimal experimental conditions. Compared with the traditional method for the visual detection of FLE, the developed QDs-ICA can successfully determine FLE residues in pork meat with a better cut-off value of 2.5 ng mL⁻¹. The QDs-ICA could be adapted for the rapid preliminary detection of FLE residues in pork meat for the first time.

(1) Water-soluble CdSe/ZnS QDs and an anti-FLE monoclonal antibody were used to prepare a fluorescent probe. (2) Primary rapid detection of FLE residues with visual fluorescent detection method.     

A label-free electrochemical platform for the highly sensitive detection of hepatitis B virus DNA using graphene quantum dots

Based on the strong interaction between single-stranded DNA and graphene material, we have designed a simple but smart electrochemical platform to detect HBV-DNA by using a graphene quantum dot (GQD) modified glassy carbon electrode coupled with specific sequence DNA molecules as probes. The probe DNA is designed to be complementary to the HBV-DNA, when the probe DNA is strongly bound to the surface of the GQD modified electrode the transfer of an electron from the electrode to the electrochemically active species K₃[Fe(CN)₆] will become difficult. Nevertheless, if the target HBV-DNA is found in the test solution, the probe DNA will bind with the target HBV-DNA instead of GQDs. As a result, the obtained peak currents of K₃[Fe(CN)₆] will have a different degree of increase with the different concentrations of the target HBV-DNA. In particular, the proposed sensor exhibits high sensitivity with a detection limit of 1 nM, and the linear detection range is from 10 nM to 500 nM. Additionally, the sensor could be used in detecting other probe DNA, which may have potential applications in the future.

Based on the interaction between single-stranded probe DNA and graphene quantum dots (GQDs), we have designed a simple but smart electrochemical platform to detect HBV-DNA by using GQDs modified glassy carbon electrode coupled with probe DNA.     

Mixture of quantum dots and ZnS nanoparticles as emissive layer for improved quantum dots light emitting diodes

Recently, quantum dots based light-emitting diodes (QLEDs) have received huge attention due to the properties of quantum dots (QDs), such as high photoluminescence quantum yield (PLQY) and narrow emission. To improve the performance of QLEDs, reducing non-radiative energy transfer is critical. So far, most conventional methods required additional chemical treatment like giant shell and/or ligands exchange. However that triggers unsought shifted emission or reduced PLQY of QDs. In this work, we have firstly suggested a novel approach to improve the efficiency of QLEDs by introducing inorganic nanoparticles (NPs) spacer between QDs, without additional chemical treatment. As ZnS NPs formed a mixture layer with QDs, the energy transfer was reduced and the distance between the QDs increased, leading to improved PLQY of mixture layer. As a result, current efficiency (CE) of the QLED device was improved by twice compared with one using only QDs layer. This is an early report on utilizing ZnS NPs as an efficient spacer, which can be utilized to other compositions of QDs.

Mixture of quantum dots and ZnS nanoparticles as emissive layer for improved QLEDs by decreasing energy transfer between the QDs.     

Construction of multifunctional carboxymethyl cellulose nanohydrogel carriers based on near-infrared DNA-templated quantum dots for tumor theranostics

Multifunctional therapeutic platforms with targeted delivery, fast diagnosis, and efficient therapy could effectively reduce side effects and improve treatment in the clinical therapy of tumors. Near-infrared DNA-templated CdTeSe quantum dots (DNA-CdTeSe QDs) were developed as building blocks to construct a multifunctional carboxymethyl cellulose (CMC)-based nanohydrogel as a nanocarrier to address the challenges of serious side effects and precise treatment in cancer theranostics, including active tumor targeting, fluorescence tracking, controlled drug release, chemotherapy and gene regulation. Single-stranded DNA containing the complementarity sequence of miRNA and cystine, as co-crosslinkers, initiated hybridization between the DNA-CdTeSe QD-modified CMC chain with the anti-nucleolin aptamer DNA (AS1411)-modified CMC chain to form the hydrogels. DOX, as a model drug, was successfully incorporated into the hydrogels. The synthesized multifunctional hydrogel nanocarriers with an average diameter of 150 nm could be taken up through targeting and achieved the controlled release of DOX by triggering both glutathione (GSH) and miRNA in the tumor microenvironment. The CdTeSe QDs trapped in nanohydrogels acted as fluorophores for bioimaging in the diagnosis and treatment process. The proposed multifunctional delivery system provided a potential platform for tumor imaging and precise therapy.

Multifunctional carboxymethyl cellulose nanohydrogel carriers for tumor theranostics.     

Highly rapid and non-enzymatic detection of cholesterol based on carbon nitride quantum dots as fluorescent nanoprobes

In this work, we reported a highly rapid and non-enzymatic method for cholesterol measuring based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes, which were synthesized through chemical oxidation. The obtained CNQDs displayed high quantum yield up to 35% as well as excellent photostability, water solubility and low toxicity. We found that the fluorescence of CNQDs could be quenched more than 90% within 30 seconds by cholesterol through the formation of hydrogen bonds between –NH₂, –NH on the surface of CNQDs and cholesterol containing –OH. According to this phenomenon, a cholesterol detection method was constructed with a wide linear region over the range of 0–500 μmol L⁻¹ and a detection limit as low as 10.93 μmol L⁻¹, and it possessed the obvious advantages of being a very rapid process and avoiding the use of enzymes. In addition, this method showed high selectivity in the presence of various interfering reagents and applicability to the measurement of cholesterol in fetal bovine serum, which indicated its potential application value in clinical settings.

Highly rapid and non-enzymatic method for the detection of cholesterol was constructed based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes. The fluorescence of CNQDs could be effectively and rapidly quenched by cholesterol.     

High efficiency blue light-emitting devices based on quantum dots with core-shell structure design and surface modification

Blue quantum dot (QD) light emitting diode (QLED) developments are far lagging behind the red and green ones as it becomes difficult to balance charge injection and photo stability than the latter. Here, we introduced a combination of a low band energy shell with better surfactants, which largely meet both abovementioned requirements. Our simulation pinpoints that it is the exposed Se on the QD surface, which causes non-radiative relaxations. By adding tributyl phosphine (TBP), which is a good ligand to Se, we recover photoluminescence quantum yield (PLQY) from less than 8.0% up to above 85.0%. The corresponding external quantum efficiency (EQE) of QLEDs increases from 3.1% to 10.1%. This demonstrates that the low bandgap shell with effective surfactant passivation is a promising strategy to enhance QLED performance.

The exposed Se on QD surface causes non-radiative relaxations which results in a low PLQY. However, the PLQY was improved from less than 8.0% up to above 85.0% by adding tributyl phosphine which can terminate the dangling bonds of the Se.