Molecularly Imprinted Viral Protein Integrated Zn-Cu-In-Se-P Quantum Dots Superlattice for Quantitative Ratiometric Electrochemical Detection of SARS-CoV-2 Spike Protein in Saliva.

Solution-processable colloidal quantum dots (QDs) are promising materials for the development of rapid and low-cost, next-generation quantum-sensing diagnostic systems. In this study, we report on the synthesis of multinary Zn-Cu-In-Se-P (ZCISeP) QDs and the application of the QDs-modified electrode (QDs/SPCE) as a solid superlattice transducer interface for the ratiometric electrochemical detection of the SARS-CoV-2-S1 protein in saliva. The ZCISeP QDs were synthesized through the formation of In(Zn)PSe QDs from InP QDs, followed by the incorporation of Cu cations into the crystal lattice via cation exchange processes. A viral-protein-imprinted polymer film was deposited onto the QDs/SPCE for the specific binding of SARS-CoV-2. Molecular imprinting of the virus protein was achieved using a surface imprinting electropolymerization strategy to create the MIP@QDs/SPCE nanosensor. Characterization through spectroscopic, microscopic, and electrochemical techniques confirmed the structural properties and electronic-band state of the ZCISeP QDs. Cyclic voltammetry studies of the QDs/SPCE superlattice confirmed efficient electron transport properties and revealed an intraband gap energy state with redox peaks attributed to the Cu1+/2+ defects. Binding of SARS-CoV-2-S1 to the MIP@QDs/SPCE cavities induced a gating effect that modulated the Fe(CN)6 3-/4- and Cu1+/2+ redox processes at the nanosensor interface, producing dual off/on ratiometric electrical current signals. Under optimal assay conditions, the nanosensor exhibited a wide linear detection range (0.001-100 pg/mL) and a low detection limit (0.34 pg/mL, 4.6 fM) for quantitative detection of SARS-CoV-2-S1 in saliva. The MIP@QDs/SPCE nanosensor demonstrated excellent selectivity against nonspecific protein targets, and the integration with a smartphone-based potentiostat confirmed the potential for point-of-care applications.

Thiolated gamma-cyclodextrin-polymer-functionalized CeFe3O4 magnetic nanocomposite as an intrinsic nanocatalyst for the selective and ultrasensitive colorimetric detection of triacetone triperoxide.

Explosives are powerful destructive weapons used by criminals and terrorists across the globe and their use within military installation sites poses serious environmental health problems. Existing colorimetric sensors for triacetone triperoxide (TATP) relies on detecting its hydrolysed H2O2 form. However, such detection strategy limits the practicability for on-site TATP sensing. In this work, we have developed a novel peroxidase mimic catalytic colorimetric sensor for direct recognition of TATP. Ceria (Ce)-doped Fe3O4 nanoparticles (CeFe3O4) were synthesized via the hot-injection organic synthetic route in the presence of metal precursors and organic ligands. Thereafter, the organic-capped CeFe3O4 nanoparticles were surface-functionalized with amphiphilic polymers (Amp-poly) to render the nanoparticle stable, compact and biocompatible. Thiolated γ-cyclodextrin (γ-CD) was adsorbed on the Amp-poly-CeFe3O4 nanocomposite (NC) surface to form a γ-CD-Amp-poly-CeFe3O4 NC. γ-CD served both as a receptor and as a catalytic enhancer for TATP. Hemin (H), used as a catalytic signal amplifier was adsorbed on the γ-CD-Amp-poly-CeFe3O4 NC surface to form a γ-CD-Amp-poly-CeFe3O4-H NC that served as a functional nanozyme for the enhanced catalytic colorimetric detection of TATP. Under optimum experimental reaction conditions, TATP prepared in BIS-TRIS-Trisma Ac-KAc-NAc buffer, pH 3, was selectively and ultrasensitively detected without the need for acid hydrolysis based on the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2 in the presence of the γ-CD-Amp-poly-CeFe3O4-H hybrid nanozyme. The obtained limit of detection of ∼0.05 µg/mL when compared with other published probes demonstrated superior sensitivity. The developed peroxidase mimic γ-CD-Amp-poly-CeFe3O4-H catalytic colorimetric sensor was successfully applied to detect TATP in soil, river water and tap water samples.

Colorimetric optical nanosensors for trace explosive detection using metal nanoparticles: advances, pitfalls, and future perspective.

Warfare threats and acts of terror are challenging situations encountered by defense agencies across the globe and are of growing concern to the general public, and security-minded policy makers. Detecting ultra-low quantities of explosive compounds in remote locations or under harsh conditions for anti-terror purposes as well as the environmental monitoring of residual or discarded explosives in soil, remains a major challenge. The use of metal nanoparticles (NPs) for trace explosive detection has drawn considerable interest in recent years. For nano-based explosive sensor devices to meet real-life operational demands, analytical parameters such as, long-shelf life, stability under harsh conditions, ease-of-use, high sensitivity, excellent selectivity, and rapid signal response must be met. Generally, the analytical performance of colorimetric-based nanosensor systems is strongly dependent on the surface properties of the nanomaterial used in the colorimetric assay. The size and shape properties of metal NPs, surface functionalisation efficiency, and assay fabrication methods, are factors that influence the efficacy of colorimetric explosive nanosensor systems. This review reports on the design and analytical performances of colorimetric explosive sensor systems using metal NPs as optical signal transducers. The challenges of trace explosive detection, advances in metal NP colorimetric explosive design, limitations of each methods, and possible strategies to mitigate the problems are discussed.

Rapid and highly selective colorimetric detection of nitrite based on the catalytic-enhanced reaction of mimetic Au nanoparticle-CeO2 nanoparticle-graphene oxide hybrid nanozyme.

The International Agency for Research cancer (IARC) has classified nitrite in Group 2A of probable carcinogens to human. Herein, we report on the rapid and selective colorimetric detection of nitrite using a chemically modified gold nanoparticle (AuNP)-cerium oxide (CeO2) NP-anchored graphene oxide (GO) hybrid nanozyme in a catalytic colorimetric assay where nitrite acts as the main oxidant/target analyte and 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate. CeO2 NPs and GO were synthesized separately and incorporated in-situ, in a synthetic solution involving the chemical reduction of Au salt to AuNPs. The chemical modification process aided the adsorption of CeO2 NPs and AuNPs on GO nanosheets, yielding a highly catalytic AuNP-CeO2 NP@GO nanohybrid material. Under optimum experimental conditions, a novel colorimetric assay for nitrite recognition was constructed in which AuNP-CeO2 NP@GO hybrid nanozyme catalysed the oxidation of TMB in the presence of nitrite prepared in a 2-(n-morpholino)ethanesulfonic acid-2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol-tris(hydroxymethyl)aminomethane acetate (MES-BIS-TRIS-Trisma Ac)-citric acid buffer solution, pH 2. Nitrite was quantitatively detected in a concentration dependent manner from 100 µM to 5000 µM with a correlation coefficient of 0.9961 and a limit of detection of 4.6 µM. Selective detection of nitrite was confirmed by the generation of a unique green colour reaction upon nitrite interaction in the AuNP-CeO2 NP@GO hybrid nanozyme redox cycle with TMB. None of the several tested metal ions and including H2O2 yielded a positive colour response, thus demonstrating the superior selectivity of the catalytic colorimetric assay for nitrite recognition. The AuNP-CeO2 NP@GO hybrid nanozyme catalytic colorimetric assay was successfully applied in the detection of nitrite in tap water.

Biomimetic graphene oxide-cationic multi-shaped gold nanoparticle-hemin hybrid nanozyme: Tuning enhanced catalytic activity for the rapid colorimetric apta-biosensing of amphetamine-type stimulants.

Amphetamine-type stimulants are a class of illicit drug that constitutes a worldwide problem to which intelligence agencies, first responders and law enforcement are tasked with identifying them in unknown samples. We report on the development of a graphene oxide (GO)-cationic multi-shaped gold nanoparticle (AuNP)-hemin hybrid nanozyme as a new biomimetic catalytic-induced aptamer-based colorimetric biosensor platform for amphetamine (AMP) and methamphetamine (MAMP). GO was electrostatically bonded to cationic multi-shaped cetyltrimethylammonium bromide (CTAB)-AuNPs to form a GO-CTAB-AuNP hybrid nanozyme exhibiting enhanced catalytic activity in the presence of hemin. The binding of an MNS 4.1 anticocaine DNA aptamer on the GO-CTAB-AuNP-hemin nanozyme assembly and the subsequent catalytic oxidation by 3,3,5,5-tetramethylbenzidine in the presence of H2O2 ensured that the colorimetric reaction was tuned to selectively detect AMP and MAMP with high sensitivity. Under optimum experimental conditions, AMP and MAMP were quantitatively detected within 1 min with a detection limit of 34.1 ng/mL and 28.6 ng/mL respectively. Selected substances and drugs, known to react positively to Marquis and Mandelin reagents (used in AMP and MAMP presumptive testing) and well-known adulterants, were tested for their affinity to react with the aptamer-based GO-CTAB-AuNP-hemin peroxidase mimic biosensor. The deep blue colorimetric reaction, specific to AMP and MAMP detection, was used as the basis to affirm the selectivity of the aptamer-based GO-CTAB-AuNP-hemin peroxidase mimic biosensor. We believe the colorimetric biosensor developed in this work demonstrates a promising new direction in presumptive testing for AMP and MAMP.

Fluorometric virus detection platform using quantum dots-gold nanocomposites optimizing the linker length variation.

In this study, a tunable biosensor using the localized surface plasmon resonance (LSPR), controlling the distance between fluorescent CdZnSeS/ZnSeS quantum dots (QDs) and gold nanoparticles (AuNPs) has been developed for the detection of virus. The distance between the AuNPs and QDs has been controlled by a linkage with a peptide chain of 18 amino acids. In the optimized condition, the fluorescent properties of the QDs have been enhanced due to the surface plasmon effect of the adjacent AuNPs. Successive virus binding on the peptide chain induces steric hindrance on the LSPR behavior and the fluorescence of QDs has been quenched. After analyzing all the possible aspect of the CdZnSeS/ZnSeS QD-peptide-AuNP nanocomposites, we have detected different concentration of influenza virus in a linear range of 10-14 to 10-9 g mL-1 with detection limit of 17.02 fg mL-1. On the basis of the obtained results, this proposed biosensor can be a good alternative for the detection of infectious viruses in the various range of sensing application.

Aptamer-based cocaine assay using a nanohybrid composed of ZnS/Ag2Se quantum dots, graphene oxide and gold nanoparticles as a fluorescent probe.

Authors report on a new fluoro-graphene-plasmonic nanohybrid aptamer-based fluorescent nanoprobe for cocaine. To construct the nanoprobe, newly synthesized glutathione-capped ZnS/Ag2Se quantum dots (QDs) were first conjugated to graphene oxide (GO) to form a QD-GO nanocomposite. The binding interaction resulted in a fluorescence turn-ON. Thereafter, cetyltrimethylammonium bromide (CTAB)-gold nanoparticles (AuNPs) were directly adsorbed on the QD-GO nanocomposite to form a novel QD-GO-CTAB-AuNP nanohybrid assembly that resulted in a fluorescence turn-OFF. Streptavidin (strep) was then adsorbed on the QDs-GO-CTAB-AuNP nanohybrid assembly which allowed binding to a biotinylated MNS 4.1 anticocaine DNA aptamer (B) receptor. The addition of cocaine into the strep-B-QDs-GO-CTAB-AuNP aptamer nanoprobe system aided affinity to the aptamer receptor and in turn turned on the fluorescence of the nanoprobe in a concentration-dependent manner. Under optimum experimental conditions, we found the strep-B-QD-GO-CTAB-AuNP to be far superior in its sensitivity to cocaine than the tested strep-B-QDs (no GO and CTAB-AuNPs), strep-B-QD-CTAB-AuNP (no GO) and strep-B-QD-GO (no CTAB-AuNP). In addition, the investigation of localized surface plasmon resonance (LSPR) amplified signal from tested plasmonic NPs shows that CTAB-AuNPs was far superior in amplifying the fluorescence signal of the nanoprobe. A detection limit of 4.6 nM (1.56 ng.mL-1), rapid response time (~2 min) and excellent selectivity against other drugs, substances and cocaine metabolites was achieved. The strep-B-QD-GO-CTAB-AuNP aptamer-based fluorescent nanoprobe was successfully applied for the determination of cocaine in seized adulterated cocaine samples. Graphical abstractSchematic representation of the streptavidin-biotin-quantum dot-graphene oxide-cetyltrimethylammonium bromide-gold nanoparticle aptamer-based fluorescent nanoprobe for cocaine.

A localized surface plasmon resonance-amplified immunofluorescence biosensor for ultrasensitive and rapid detection of nonstructural protein 1 of Zika virus.

Among the members of flaviviruses, the Zika virus (ZIKV) remains a potent infectious disease agent, with its associated pandemic prompting the World Health Organization (WHO) to declare it a global public health concern. Thus, rapid and accurate diagnosis of the ZIKV is needed. In this study, we report a new immunofluorescence biosensor for the detection of nonstructural protein 1 (NS1) of the ZIKV, which operates using the localized surface plasmon resonance (LSPR) signal from plasmonic gold nanoparticles (AuNPs) to amplify the fluorescence intensity signal of quantum dots (QDs) within an antigen-antibody detection process. The LSPR signal from the AuNPs was used to amplify the fluorescence intensity of the QDs. For ultrasensitive, rapid, and quantitative detection of NS1 of the ZIKV, four different thiol-capped AuNPs were investigated. Our biosensor could detect the ZIKV in a wide concentration range from 10-107 RNA copies/mL, and we found that the limit of detection (LOD) for the ZIKV followed the order Ab-L-cysteine-AuNPs (LOD = 8.2 copies/mL) > Ab-3-mercaptopropionic acid-AuNPs (LOD = 35.0 copies/mL). Immunofluorescence biosensor for NS1 exhibited excellent specificity against other negative control targets and could also detect the ZIKV in human serum.

High-Performance Biosensing Systems Based on Various Nanomaterials as Signal Transducers.

Recently, highly sensitive and selective biosensors have become necessary for improving public health and well-being. To fulfill this need, high-performance biosensing systems based on various nanomaterials, such as nanoparticles, carbon nanomaterials, and hybrid nanomaterials, are developed. Numerous nanomaterials show excellent physical properties, including plasmonic, magnetic, catalytic, mechanical and fluorescence properties and high electrical conductivities, and these unique and beneficial properties have contributed to the fabrication of high-performance biosensors with various applications, including in optical, electrical, and electrochemical detection platforms. In addition, these properties can be transformed to signals for the detection of biomolecules. In this review, various types of nanomaterial-based biosensors are introduced, and they show high sensitivity and selectivity. In addition, the potential applications of these sensors on the biosensing of several types of biomolecules are also discussed. These nanomaterials-based biosensing systems provide a significant improvement on healthcare including rapid monitoring and early detection of infectious disease for public health.

Single-step detection of norovirus tuning localized surface plasmon resonance-induced optical signal between gold nanoparticles and quantum dots.

A new method of label free sensing approach with superior selectivity and sensitivity towards virlabel-freeon is presented here, employing the localized surface plasmon resonance (LSPR) behavior of gold nanoparticles (AuNPs) and fluorescent CdSeTeS quantum dots (QDs). Inorganic quaternary alloyed CdSeTeS QDs were capped with L-cysteine via a ligand exchange reaction. Alternatively, citrate stabilized AuNPs were functionalized with 11-mercaptoundecanoic acid to generate carboxylic group on the gold surface. The carboxylic group on the AuNPs was subjected to bind covalently with the amine group of L-cysteine capped CdSeTeS QDs to form CdSeTeS QDs/AuNPs nanocomposites. The fluorescence of CdSeTeS QDs/AuNPs nanocomposite shows quenched spectrum of CdSeTeS QDs at 640 nm due to the close interaction with AuNPs. However, after successive addition of norovirus-like particles (NoV-LPs), steric hindrance-induced LSPR signal from the adjacent AuNPs triggered the fluorescence enhancement of QDs in proportion to the concentration of the target NoV-LPs. A linear range of 10-14 to 10-9 g mL-1 NoV-LPs with a detection limit of 12.1 × 10-15 g mL-1 was obtained. This method was further applied on clinically isolated norovirus detection, in the range of 102-105 copies mL-1 with a detection limit of 95.0 copies mL-1, which is 100-fold higher than commercial ELISA kit. The superiority of the proposed sensor over other conventional sensors is found in its ultrasensitive detectability at low virus concentration even in clinically isolated samples. This proposed detection method can pave an avenue for the development of high performance and robust sensing probes for detection of virus in biomedical applications.

Plasmonic Oleylamine-Capped Gold and Silver Nanoparticle-Assisted Synthesis of Luminescent Alloyed CdZnSeS Quantum Dots.

We report on a novel strategy to tune the structural and optical properties of luminescent alloyed quantum dot (QD) nanocrystals using plasmonic gold (Au) and silver (Ag) nanoparticles (NPs). Alloyed CdZnSeS QDs were synthesized via the organometallic synthetic route with different fabrication strategies that involve alternative utilization of blends of organic surfactants, ligands, capping agents, and plasmonic oleylamine (OLA)-functionalized AuNPs and AgNPs. Ligand exchange with thiol l-cysteine (l-cyst) was used to prepare the hydrophilic nanocrystals. Analysis of the structural properties using powder X-ray diffraction revealed that under the same experimental condition, the plasmonic NPs altered the diffractive crystal structure of the alloyed QDs. Depending on the fabrication strategy, the crystal nature of OLA-AuNP-assisted CdZnSeS QDs was a pure hexagonal wurtzite domain and a cubic zinc-blende domain, whereas the diffraction pattern of OLA-AgNP-assisted CdZnSeS QDs was dominantly a cubic zinc-blende domain. Insights into the growth morphology of the QDs revealed a steady transformation from a heterogeneous growth pattern to a homogenous growth pattern that was strongly influenced by the plasmonic NPs. Tuning the optical properties of the alloyed QDs via plasmonic optical engineering showed that the photoluminescence (PL) quantum yield (QY) of the AuNP-assisted l-cyst-CdZnSeS QDs was tuned from 10 to 31%, whereas the PL QY of the AgNP-assisted l-cyst-CdZnSeS QDs was tuned from 15 to 90%. The low PL QY was associated with the surface defect state, while the remarkably high PL QY exhibited by the AgNP-assisted l-cyst-CdZnSeS QDs lends strong affirmation that the fabrication strategy employed in this work provides a unique opportunity to create single ensemble, multifunctional, highly fluorescent alloyed QDs for tailored biological applications.

Localized surface plasmon resonance-mediated fluorescence signals in plasmonic nanoparticle-quantum dot hybrids for ultrasensitive Zika virus RNA detection via hairpin hybridization assays.

The current epidemic caused by the Zika virus (ZIKV) and the devastating effects of this virus on fetal development, which result in an increased incidence of congenital microcephaly symptoms, have prompted the World Health Organization (WHO) to declare the ZIKV a public health issue of global concern. Efficient probes that offer high detection sensitivity and specificity are urgently required to aid in the point-of-care treatment of the virus. In this study, we show that localized surface plasmon resonance (LSPR) signals from plasmonic nanoparticles (NPs) can be used to mediate the fluorescence signal from semiconductor quantum dot (Qdot) nanocrystals in a molecular beacon (MB) biosensor probe for ZIKV RNA detection. Four different plasmonic NPs functionalized with 3-mercaptopropionic acid (MPA), namely MPA-AgNPs, MPA-AuNPs, core/shell (CS) Au/AgNPs, and alloyed AuAgNPs, were synthesized and conjugated to L-glutathione-capped CdSeS alloyed Qdots to form the respective LSPR-mediated fluorescence nanohybrid. The concept of the plasmonic NP-Qdot-MB biosensor involves using LSPR from the plasmonic NPs to mediate a fluorescence signal to the Qdots, triggered by the hybridization of the target ZIKV RNA with the DNA loop sequence of the MB. The extent of the fluorescence enhancement based on ZIKV RNA detection was proportional to the LSPR-mediated fluorescence signal. The limits of detection (LODs) of the nanohybrids were as follows: alloyed AuAgNP-Qdot646-MB (1.7 copies/mL)) > CS Au/AgNP-Qdot646-MB (LOD =2.4 copies/mL) > AuNP-Qdot646-MB (LOD =2.9 copies/mL) > AgNP-Qdot646-MB (LOD =7.6 copies/mL). The LSPR-mediated fluorescence signal was stronger for the bimetallic plasmonic NP-Qdots than the single metallic plasmonic NP-Qdots. The plasmonic NP-Qdot-MB biosensor probes exhibited excellent selectivity toward ZIKV RNA and could serve as potential diagnostic probes for the point-of care detection of the virus.

Bright luminescent optically engineered core/alloyed shell quantum dots: an ultrasensitive signal transducer for dengue virus RNA via localized surface plasmon resonance-induced hairpin hybridization.

Novel probes that can accurately (with sensitivity and specificity) detect and discriminate between the various serotypes of dengue virus (DENV) are needed for point-of-care treatment. The efficacy of a fluorophore reporter at optically transducing an ultrasensitive fluorescence intensity signal for a target nucleic acid within a molecular beacon (MB) biosensor system depends primarily on its optical properties. A new class of bright luminescent and size-dependent glutathione (GSH)-functionalized CdSe/ZnSeS core/alloyed shell quantum dots (Qdots) have been synthesized and characterized. Shell alloying tuned the photoluminescence (PL) quantum yield within the range of 23-99%, representing an approximately 2-8-fold increase over that of the binary CdSe core. In the first step of the biosensor design, gold nanoparticles (AuNPs) were conjugated to the Qdots to form AuNP-Qdot nanohybrids. In the second step, the AuNP-Qdot nanohybrids were conjugated to the 5' end of the MB. Despite the strong binding of the entities, both the AuNP-Qdot and AuNP-Qdot-MB conjugates maintained high colloidal stability. Nucleic acids of DENV1-4 were detected by the AuNP-Qdot-MB biosensors with high sensitivity, with the detection limits of the serotypes ranging from 31-260 copies per mL. The biosensor specifically discriminated between each serotype of the virus. A sensitivity comparison of a Qdot-MB with the AuNP-Qdot-MB showed that the localized surface plasmon resonance-induced signal from the AuNPs to the fluorescence intensity of the Qdots enhanced the performance of the biosensor. We have developed a new AuNP-Qdot-MB biosensor for DENV possessing high sensitivity and specificity. The new ultrasensitive assay holds great promise for the specific diagnosis of DENV, while the versatile biosensor concept is applicable to any type of RNA virus.

Versatility of a localized surface plasmon resonance-based gold nanoparticle-alloyed quantum dot nanobiosensor for immunofluorescence detection of viruses.

Flu infection, caused by the influenza virus, constitutes a serious threat to human lives worldwide. A rapid, sensitive and specific diagnosis is urgently needed for point-of-care treatment and to control the rapid spread of this disease. In this study, an ultrasensitive, rapid and specific localized surface plasmon resonance (LSPR)-induced immunofluorescence nanobiosensor has been developed for the influenza virus based on a gold nanoparticle (AuNP)-induced quantum dot (QD) fluorescence signal. Alloyed quaternary CdSeTeS QDs were synthesized via the hot-injection organometallic route and were subsequently capped with l-cysteine via a ligand exchange reaction. AuNPs were synthesized in HEPES buffer and thiolated with l-cysteine. The concept of the biosensor involves the conjugation of anti-neuraminidase (NA) antibody (anti-NA Ab) to thiolated AuNPs and the conjugation of anti-hemagglutinin (HA) antibody (anti-HA Ab) to alloyed quaternary l-cysteine-capped CdSeTeS QDs. Interaction of the antigens displaying on the surface of the influenza virus target with anti-NA Ab-conjugated AuNPs and anti-HA Ab-conjugated QDs induces an LSPR signal from adjacent AuNPs to trigger fluorescence-enhancement changes in the QDs in proportion to the concentration of the target virus. The detection limit for influenza H1N1 virus was 0.03pg/mL in deionized water and 0.4pg/mL in human serum; while, for the clinically isolated H3N2, the detection limit was 10PFU/mL. The detection of influenza virus H1N1 was accomplished with high sensitivity. The versatility of the biosensor was demonstrated for the detection of clinically isolated influenza virus H3N2 and norovirus-like particles (NoV-LPs).

Gold Nanoparticle-Quantum Dot Fluorescent Nanohybrid: Application for Localized Surface Plasmon Resonance-induced Molecular Beacon Ultrasensitive DNA Detection.

In biosensor design, localized surface plasmon resonance (LSPR)-induced signal from gold nanoparticle (AuNP)-conjugated reporter can produce highly sensitive nanohybrid systems. In order to retain the physicochemical properties of AuNPs upon conjugation, high colloidal stability in aqueous solution is needed. In this work, the colloidal stability with respect to the zeta potential (ZP) of four negatively charged thiol-functionalized AuNPs, thioglycolic (TGA)-AuNPs, 3-mercaptopropionic acid (MPA)-AuNPs, L-cysteine-AuNPs and L-glutathione (GSH)-AuNPs, and a cationic cyteamine-capped AuNPs was studied at various pHs, ionic strength, and NP concentration. A strong dependence of the ZP charge on the nanoparticle (NP) concentration was observed. High colloidal stability was exhibited between pH 3 and 9 for the negatively charged AuNPs and between pH 3 and 7 for the cationic AuNPs. With respect to the ionic strength, high colloidal stability was exhibited at ≤104 µM for TGA-AuNPs, L-cysteine-AuNPs, and GSH-AuNPs, whereas ≤103 µM is recommended for MPA-AuNPs. For the cationic AuNPs, very low ionic strength of ≤10 µM is recommended due to deprotonation at higher concentration. GSH-AuNPs were thereafter bonded to SiO2-functionalized alloyed CdZnSeS/ZnSe1.0S1.3 quantum dots (SiO2-Qdots) to form a plasmon-enhanced AuNP-SiO2-Qdots fluorescent nanohybrid. The AuNP-SiO2-Qdots conjugate was afterward conjugated to a molecular beacon (MB), thus forming an ultrasensitive LSPR-induced SiO2-Qdots-MB biosensor probe that detected a perfect nucleotide DNA sequence at a concentration as low as 10 fg/mL. The limit of detection was ~11 fg/mL (1.4 fM) while the biosensor probe efficiently distinguished between single-base mismatch and noncomplementary sequence target.

Size-confined fixed-composition and composition-dependent engineered band gap alloying induces different internal structures in L-cysteine-capped alloyed quaternary CdZnTeS quantum dots.

The development of alloyed quantum dot (QD) nanocrystals with attractive optical properties for a wide array of chemical and biological applications is a growing research field. In this work, size-tunable engineered band gap composition-dependent alloying and fixed-composition alloying were employed to fabricate new L-cysteine-capped alloyed quaternary CdZnTeS QDs exhibiting different internal structures. Lattice parameters simulated based on powder X-ray diffraction (PXRD) revealed the internal structure of the composition-dependent alloyed CdxZnyTeS QDs to have a gradient nature, whereas the fixed-composition alloyed QDs exhibited a homogenous internal structure. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analysis confirmed the size-confined nature and monodispersity of the alloyed nanocrystals. The zeta potential values were within the accepted range of colloidal stability. Circular dichroism (CD) analysis showed that the surface-capped L-cysteine ligand induced electronic and conformational chiroptical changes in the alloyed nanocrystals. The photoluminescence (PL) quantum yield (QY) values of the gradient alloyed QDs were 27-61%, whereas for the homogenous alloyed QDs, the PL QY values were spectacularly high (72-93%). Our work demonstrates that engineered fixed alloying produces homogenous QD nanocrystals with higher PL QY than composition-dependent alloying.

An ultrasensitive SiO2-encapsulated alloyed CdZnSeS quantum dot-molecular beacon nanobiosensor for norovirus.

Ultrasensitive, rapid and selective diagnostic probes are urgently needed to overcome the limitations of traditional probes for norovirus (NV). Here, we report the detection of NV genogroup II via nucleic acid hybridization technology using a quantum dot (QD)-conjugated molecular beacon (MB) probe. To boost the sensitivity of the MB assay system, an ultrasensitive QD fluorophore with unique optical properties was synthesized, characterized and exploited as a fluorescence signal generator. Alloyed thioglycolic (TGA)-capped CdZnSeS QDs with a high photoluminescence (PL) quantum yield (QY) value of 92% were synthesized, and a modified silanization method was employed to encapsulate the thiol-capped QDs in a silica layer. The resulting highly luminescent alloyed SiO2-coated CdZnSeS QDs had a remarkable PL QY value of 98%. Transmission electron microscopy and dynamic light scattering confirmed the monodispersity of the alloyed nanocrystals, and zeta potential analysis confirmed their colloidal stability. Powder X-ray diffraction and PL lifetime measurements confirmed the surface modification of the QDs. The alloyed TGA-capped and SiO2-coated CdZnSeS QD-conjugated MB bioprobes detected extremely low concentrations of NV RNA. Ultrasensitive detection of low concentrations of NV RNA with a limit of detection (LOD) of 8.2copies/mL in human serum and a LOD of 9.3 copies/mL in buffer was achieved using the SiO2-coated CdZnSeS QD-MB probes, an increase in sensitivity of 3-fold compared with the detection limit for NV RNA using TGA-capped CdZnSeS QD-MBs. The additional merits of our detection system are rapidity, specificity and improved sensitivity over conventional molecular test probes.

An ultrasensitive alloyed near-infrared quinternary quantum dot-molecular beacon nanodiagnostic bioprobe for influenza virus RNA.

Conventional techniques used to diagnose influenza virus face several challenges, such as low sensitivity, slow detection, false positive results and misinterpreted data. Hence, diagnostic probes that can offer robust detection qualities, such as high sensitivity, rapid detection, elimination of false positive data, and specificity for influenza virus, are urgently needed. The near-infrared (NIR) range is an attractive spectral window due to low photon absorption by biological tissues, hence well-constructed fluorescent biosensors that emit within the NIR window can offer an improved limit of detection (LOD). Here, we demonstrate the use of a newly synthesized NIR quinternary alloyed CdZnSeTeS quantum dots (QDs) as an ultrasensitive fluorescence reporter in a conjugated molecular beacon (MB) assay to detect extremely low concentrations of influenza virus H1N1 RNA. Under optimum conditions, two different strains of influenza virus H1N1 RNA were detected based on fluorescence enhancement signal transduction. We successfully discriminated between two different strains of influenza virus H1N1 RNA based on the number of complementary nucleotide base pairs of the MB to the target RNA sequence. The merits of our bioprobe system are rapid detection, high sensitivity (detects H1N1 viral RNA down to 2 copies/mL), specificity and versatility (detects H1N1 viral RNA in human serum). For comparison, a conventional CdSe/ZnS-MB probe could not detect the extremely low concentrations of H1N1 viral RNA detected by our NIR alloyed CdZnSeTeS-MB probe. Our bioprobe detection system produced a LOD as low as ~1 copy/mL and is more sensitive than conventional molecular tests and rapid influenza detection tests (RIDTS) probes.

Gradient band gap engineered alloyed quaternary/ternary CdZnSeS/ZnSeS quantum dots: an ultrasensitive fluorescence reporter in a conjugated molecular beacon system for the biosensing of influenza virus RNA.

Controlling and engineering the particle composition of semiconductor alloys is one of the topmost targets in the field of semiconductor materials science and technology. Quantum dot (QD) nanocrystals offer an unmatched opportunity to obtain a wide range of composition-controlled alloys and have captivated a great deal of interest recently. Herein, we report on band gap engineering via tuning and controlling the sulphur molar fraction (ternary shell layer) of quaternary/ternary core/shell alloyed CdZnSeS/ZnSeS QDs. Varying optical properties were exhibited by the alloyed QDs but a uniform particle size distribution was maintained across all the compositions. The alloyed QDs displayed bright emission colours under UV irradiation, whereas the photoluminescence quantum yields (PL QY) were in a remarkable range of 36-98%. Non-linearity of the lattice parameter was an indication of gradient alloying of the nanocrystals, whereas the kinetics of the optical properties unravelled the effect of intrinsic optical bowing. Displacement of bond length and anion mismatch influenced the optical properties of the QDs with respect to the variation in the PL QY. Alloyed CdZnSeS/ZnSe1.0S1.3 QDs with a spectacular PL QY were exploited as an ultrasensitive fluorescence reporter in a conjugated molecular beacon (MB) assay to detect influenza virus H1N1 RNA. Our detection system was rapid and highly sensitive for detecting extremely low concentrations of H1N1 RNA (down to 2 copies per mL), specific and versatile (detects H1N1 RNA in human serum). For proof of concept, the alloyed CdZnSeS/ZnSe1.0S1.3 QD-MB bioprobe exhibited a superior 12-fold sensitivity over an alloyed CdZnSeS-MB probe, while a conventional CdSe/ZnS-MB probe could not detect extremely low concentrations of influenza virus H1N1 RNA.

Deposition of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shells around CdSeTe alloyed core quantum dots: effects on optical properties.

In this work, we synthesized water-soluble L-cysteine-capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time-resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs.