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In response to the growing demand for biomolecular diagnostics, metasurface (MS) platforms based on high-Q resonators have demonstrated their capability to detect analytes with smart data processing and image analysis technologies. However, high-Q resonator meta-atom arrays are highly sensitive to the fabrication process and chemical surface functionalization. Thus, spectrum scanning systems are required to monitor the resonant wavelength changes at every step, from fabrication to practical sensing. In this study, we propose an innovative dielectric resonator-independent MS platform that enables spectrometer-less biomolecule detection using artificial intelligence (AI) at a visible wavelength. Functionalizing the focused vortex MS to capture gold nanoparticle (AuNP)-based sandwich immunoassays causes the resulting vortex beam profiles to be significantly affected by the localized surface plasmon resonance (LSPR) occurring between AuNPs and meta-atoms. The convolutional neural network algorithm was carefully trained to accurately classify the AuNP concentration-dependent focused vortex beam, facilitating the determination of the concentration of the targeted diagnostic biomolecule. Successful in situ identification of various biomolecule concentrations was achieved with over 99 % accuracy, indicating the potential of combining an LSPR-susceptible MS platform and AI for continuously tracking various chemical and biological compounds., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The current study intended to evaluate two types of biorecognition element (BRE), namely recombinant antibody fragments and M13 bacteriophage-displayed antibody fragments, where protein L and electrostatic interactions were used to respectively conjugated antibodies and bacteriophages on AuNPs. The functionalization process was examined by DLS to monitor the changes in the size and zeta potential. The formation of the BRE-G17-Gly immunological complexes was manifested by aggregation (confirmed by FE-SEM) and color change from red to dark blue visible to the naked eye. Local refractive index variations of functionalized AuNPs were monitored by a UV - vis spectrophotometer, showing increasing size and decreasing zeta potential in all stages. The calibration plot was developed in the concentration range 1-5 µg/mL and the limit of detection (LOD) was 1 µg/mL. The LSRP nanobiosensor in combination with the phage-based BRE was an affordable and simple approach, as it was able to eliminate the time-consuming and costly step of extracting antibodies. Contrary to the traditional immunoassays, this method does not require additional amplification, e.g., enzymatic, to read the result. The proposed LSPR nanobiosensor model can be adapted to detect a wide range of pathogens, viruses, and biomarkers in the shortest possible time., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A new biosensing method is presented to detect gene mutation by integrating the MutS protein from bacteria with a fiber optic particle plasmon resonance (FOPPR) sensing system. In this method, the MutS protein is conjugated with gold nanoparticles (AuNPs) deposited on an optical fiber core surface. The target double-stranded DNA containing an A and C mismatched base pair in a sample can be captured by the MutS protein, causing increased absorption of green light launching into the fiber and hence a decrease in transmitted light intensity through the fiber. As the signal change is enhanced through consecutive total internal reflections along the fiber, the limit of detection for an AC mismatch heteroduplex DNA can be as low as 0.49 nM. Because a microfluidic chip is used to contain the optical fiber, the narrow channel width allows an analysis time as short as 15 min. Furthermore, the label-free and real-time nature of the FOPPR sensing system enables determination of binding affinity and kinetics between MutS and single-base mismatched DNA. The method has been validated using a heterozygous PCR sample from a patient to determine the allelic fraction. The obtained allelic fraction of 0.474 reasonably agrees with the expected allelic fraction of 0.5. Therefore, the MutS-functionalized FOPPR sensor may potentially provide a convenient quantitative tool to detect single nucleotide polymorphisms in biological samples with a short analysis time at the point-of-care sites.

A greener approach for the design of surface plasmon resonant gold nanoparticles has been obtained with a hydrosoluble fraction of an endemic asteraceae medicinal plant. This medicinal plant is originated from Indian Ocean and demonstrates its bioreducing activity in the design of stable green nanomedicine in aqueous media. This article describes the preclinical assessment of the efficacy of these novel nanocandidates on murine model by intratumoral and intravenous injections. It definitely demonstrates two key points in the treatment of cancer: 1) optimization of the tumor microenvironment targeting by specific ligands for a limited damage on healthy tissue, 2) the need to screen the specific irradiation dose (time, power) taking into account the type of tumor., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Fibrinogen, which is a glycoprotein that circulates in the blood, plays various important biological roles, e.g., in blood coagulation, fibroblast proliferation, angiogenesis, and wound healing. Abnormal levels of fibrinogen in plasma have been identified as a key biomarker of a variety of disorders from cardiovascular diseases to hemophilia. Therefore, the development of a quantitative assay for fibrinogen in the blood has emerged as an important issue for the prevention and diagnosis of these diseases. Meanwhile, it is well known that erythrocytes can selectively capture fibrinogen because of the fibrinogen receptor expressed on their plasma membrane. Inspired by these biological interactions, herein, we devised an erythrocyte membrane (EM)-blanketed biosensor based on localized surface plasmon resonance (LSPR) for highly sensitive detection of fibrinogen. By placing the EM onto a nanoparticle-on-substrate, we enhanced the LSPR signal, achieving highly sensitive and selective detection of fibrinogen. We demonstrated that fibrinogen detection is possible over a wide concentration range, 0.001-5.000 mg/mL, which can cover normal and pathological blood fibrinogen levels. In addition, it was verified that the biosensor selectively detects fibrinogen in comparison with other human-blood-plasma components. The nanoplasmonic sensor blanketed with the EM opens up new opportunities for the development of a robust fibrinogen-sensing technology., (Copyright © 2019 Elsevier B.V. All rights reserved.)

α-Cyclopiazonic acid (CPA) is a tremorgenic mycotoxin produced by Aspergillus and Penicillium fungal species, commonly found on agricultural commodities or fermented food products. A sensitive and rapid imaging surface plasmon resonance (iSPR) assay was developed to detect CPA in maize and cheese by combining an indirect competitive immunoassay and signal amplification based upon a secondary antibody (Ab 2 ) conjugated with gold nanoparticles. Matrix-matched calibration curves were used to determine CPA content in maize and cheese samples. Recoveries, at two spiking levels in maize and cheese, were 89 to 126%, with standard deviations of repeatability (RSDr) of less than 16%. The limits of detection were 17 and 6 μg/kg in maize and cheese, respectively. To separate the CPA-contaminated samples from uncontaminated samples, a cutoff validation level of 40 μg/kg was introduced. The assay was applied to samples of naturally contaminated maize and was compared with competitive inhibition enzyme-linked immunosorbent assay (CI-ELISA). This is the first report to detect CPA using an immuno-biosensor iSPR format.

Current techniques for plant virus detection, such as RT- PCR and ELISA, require multistep procedures and rely on sophisticated equipment. Due to the global spread of plant viruses, the development of simpler, faster and cheaper assay methods is inevitable. Gold nanoparticles (AuNPs) had raised much interest during recent years due to their novel optical properties or diagnostic purposes. The localized surface plasmon resonance (LSPR 1 ) of AuNPs had been used in the development of novel colorimetric nano-biosensing systems. The frequency and intensity of the LSPR peak generally depend on the shape, size and the surrounding medium of the AuNPs. In this study, unmodified AuNPs had been used to detect the unamplified Tomato yellow leaf curl virus (TYLCV) genome in infected plants. A specific DNA probe complementary to the coat protein region of virus genome was designed. The extracted total DNA of uninfected and infected plants was mixed with hybridization buffer and the designed probe. The mixture was denatured, annealed and then cooled to room temperature and was followed by AuNPs addition. The color changes in the samples indicating the presence of target virus infections were assessed visually after the addition of salt and confirmed by UV-Vis spectroscopy. The results showed that this strategy allowed for fast and sensitive detection of TYLCV genome and eliminated the need for PCR amplification and detection equipment., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Dense arrays of well-dispersed gold nanoparticles (AuNPs) on optical fibers are shown to bridge the gap in sensitivity and sensing performance between localized surface plasmon resonance (LSPR) and classical SPR sensing. A simple self-assembly method relying on a poly(styrene- b-4-vinylpyridine) (PS- b-P4VP) block copolymer brush layer was used to immobilize AuNPs of different diameters from 10 to 92 nm on optical fibers. In comparison with standard AuNP deposition methods using (3-aminopropyl)trimethoxysilane (APTMS) and polyelectrolytes, the sensitivity with the PS- b-P4VP templating method was found to be 3-fold better, a consequence of the smaller gap between particles and the presence of fewer AuNP aggregates. Hence, the sensitivity of the LSPR sensor for IgG was comparable to a classical SPR, also on optical fibers, and about 68% of that for a prism-based wavelength-interrogation SPR instrument. The reproducibility and the detection limit of the LSPR sensor were about the same as the SPR sensor. The enhanced performance of the LSPR sensors using the PS- b-P4VP block copolymer fabrication method paves the way for use of these LSPR biosensors in a smaller and more cost-effective platform.

This study reports a colorimetric sensor with excellent sensitivity to detect Cefixime base on gold nanoparticles. Cefixime is an antibiotic which has a wide range of applications in medicine. Cefixime did not change the surface plasmon resonance bond in gold nanoparticles solution; therefore, there was no change in the color solution of gold nanoparticles. The presence of Alizarin Red S in the system was necessary for the degradation of Cefixime, resulting in the aggregation of gold nanoparticles and a color change from red to blue. As a result of aggregation, the localized surface plasmon resonance band of gold nanoparticles decreased to around 525 nm and a new red-shifted band at 640 nm appeared which increases gradually as the function of Cefixime concentration. A unique detection limit (2.5 ng mL -1 ) was achieved for Cefixime in comparison with other colorimetric methods. Relative standard deviations (RSD) for 40.0 and 140.0 ng mL -1 of Cefixime were 2.6 and 1.8% for intra-day respectively. A possible mechanism was discussed for the surface plasmon resonance changes of AuNPs in the presence of Cefixime. The proposed method was applied to detect Cefixime in pharmaceutical samples with satisfactory results. This system is low-cost and is highly sensitive with no need for any preconcentration steps or using any expensive or sophisticated instrumentation., (Copyright © 2018. Published by Elsevier B.V.)

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 10 2 -10 5 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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A rapid, sensitive and multiplexed imaging surface plasmon resonance (iSPR) biosensor assay was developed and validated for three Fusarium toxins, deoxynivalenol (DON), zearalenone (ZEA) and T-2 toxin. The iSPR assay was based on a competitive inhibition format with secondary antibodies (Ab 2 ) conjugated to gold nanoparticles (AuNPs) used as a signal amplification tag. Signal was amplified nearly 25-fold for DON, 90-fold for ZEA and 12-fold for T-2 toxin assay using Ab 2 -AuNPs. Analyses, including steps to regenerate the sensor, took 17.5min. The antigen coated sensor chip was used for more than 46 cycles without affecting signal intensity (< 12%). Matrix matched calibration curves were used to determine Fusarium toxins in wheat. The mean recoveries ranged from 87% to 103% with relative standard deviations of repeatability of less than 5%. The limits of detection were 15µg/kg for DON, 24µg/kg for ZEA and 12µg/kg for T-2 toxin. This provided sufficient sensitivity to monitor contamination of these mycotoxins in wheat in accordance with European Commission (EC) limits. Cut off levels for all three Fusarium toxins were validated using blank wheat and wheat spiked either at the EC regulated levels (100µg/kg for ZEA and T-2 toxin) or at one third of the EC level (for DON: 400µg/kg). The assay was successfully applied and further validated with naturally contaminated wheat samples. This is the first reported AuNP enhanced iSPR assay to detect and classify three agriculturally important Fusarium toxins in wheat., (Published by Elsevier B.V.)

Biosensor for the detection of virus was developed by utilizing plasmonic peak shift phenomenon of the gold nanoparticles and viral infection mechanism of hemagglutinin on virus and sialic acid on animal cells. The plasmonic peak of the colloidal gold nanoparticles changes with the aggregation of the particles due to the plasmonic interaction between nearby particles and the color of the colloidal nanoparticle solution changes from wine red to purple. Sialic acid reduced and stabilized colloidal gold nanoparticle aggregation is induced by the addition of viral particles in the solution due to the hemagglutinin-sialic acid interaction. In this work, sialic acid reduced and stabilized gold nanoparticles (d = 20.1 ± 1.8 nm) were synthesized by a simple one-pot, green method without chemically modifying sialic acid. The gold nanoparticles showed target-specific aggregation with viral particles via hemagglutinin-sialic acid binding. A linear correlation was observed between the change in optical density and dilution of chemically inactivated influenza B virus species. The detection limit of the virus dilution (hemagglutinination assay titer, 512) was shown to be 0.156 vol% and the upper limit of the linearity can be extended with the use of more sialic acid-gold nanoparticles.

A highly sensitive and simple indirect spectrophotometric method has been developed for the determination of trace amounts of inorganic mercury (Hg(2+)) in aqueous media. The method is based on the inhibitory effect of Hg(2+) on the activity of horseradish peroxidase (HRP) in the oxidation of ascorbic acid by hydrogen peroxide followed by the reduction of Au(3+) to Au-NPs by unreacted ascorbic acid and the measurement of the absorbance of localized surface plasmon resonance (LSPR) peak of gold nanoparticles (at 530 nm) which is directly proportional to the concentration of Hg(2+). Under the optimum conditions, the calibration curve was linear in the concentration range of 1-220 ng mL(-1). Limits of detection (LOD) and quantification (LOQ) were 0.2 and 0.7 ng mL(-1), respectively and the relative standard deviation at 100 ng mL(-1) level of Hg(2+) was 2.6%. The method was successfully applied to the determination of mercury in different water samples., (Copyright © 2015 Elsevier B.V. All rights reserved.)

We present the design and experimental verification of a self-referencing dual-channel fiber optic particle plasmon resonance (FOPPR) sensing system for compensation of thermal and bulk-composition effects as well as nonspecific adsorption in real-time biosensing of complex samples. A theoretical model is first proposed and then a systematic experimental approach is used to verify the model. The sensing system comprises an analysis fiber sensor and a reference fiber sensor in a single microfluidic chip, where the analysis fiber is functionalized with a recognition molecule. The compensation still works even if the surface coverages of gold nanoparticles on the reference and analysis fibers are not exactly the same. The potential of this approach is illustrated by a model biosensing experiment in which the detection of anti-biotin is compensated for bulk refractive index change, nonspecific adsorption and/or color interference, in various sample media. The percent recovery is 103.2% under both the effects of bulk refractive index change and nonspecific adsorption and is 93.9% under both the effects of color interference and nonspecific adsorption, suggesting that the compensation is effective., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Rapid and sensitive methodologies for the detection of protein are in urgent requirement for clinic diagnostics. Localized surface plasmon resonance (LSPR) of metal nanostructures has the potential to circumvent this problem due to its sensitive optical properties and strong electromagnetic near-field enhancements. In this work, an enzyme mediated plasmonic biosensor on the basis of a dual-functional nanohybrid was developed for the detection of thrombin. By utilizing LSPR-responsive nanohybrid and anaptamer-enzyme conjugated reporting probe, the sensing platform brings enhanced signal, stability as well as simplicity. Enzymatic reaction catalyzed the reduction of Au(3+) to Au° in situ, further leading to the rapid crystal growth of gold nanoparticles (AuNPs). The LSPR absorbance band and color changed company with the nanoparticle generation, which can be real-time monitoring by UV-visible spectrophotometer and naked eye. Nanohybrid constructed by gold and magnetic nanoparticles acts as a dual functional plasmonic unit, which not only plays the role of signal production, but also endows the sensor with the function of magnetic separation. Simultaneously, the introduction of enzyme effectively regulates the programming crystal growth of AuNPs. In addition, enzyme also serves as signal amplifier owing to its high catalysis efficiency. The response of the plasmonic sensor varies linearly with the logarithmic thrombin concentration up to 10nM with a limit of detection of 200 pM. The as-proposed strategy shows good analytical performance for thrombin determination. This simple, disposable method is promising in developing universal platforms for protein monitoring, drug discovery and point-of-care diagnostics., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In the field of nucleic acid-based biosensor technology, DNA-conjugated nanocomposites have attracted much attention due to their unique properties and multimodal applicability. However, quantitative estimation of sequence-specific oligonucleotide in a simpler way is still a challenge. Precise positioning of DNA probes over the surface of the nanocomposite can overcome problems such as steric hindrance of the surface-bound molecules to enable further sensing as well as nonspecific folding of the DNA molecule over the surface of the gold (Au) nanolayer. Considering such objectives, we have developed glutathionated Fe3O4@Au core/shell nanocomposite, fabricated with DNA molecules and applied for sensing complementary oligo spectrophotometrically, using the localized surface plasmon resonance (LSPR) properties of the synthesized nanocomposite. When hybridization experiments were performed with 10 to 100 fM complementary DNA and DNA-conjugated nanocomposite, a strong linear relationship was observed between DNA concentration and surface plasmon resonance (SPR). Discrimination even at the single-base level was also observed when further experiments were performed with complementary DNA, but with a sequential decrease of bases from the single level to the fifth level., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Surface plasmon resonance imaging (SPRi) is an intriguing technique for immunoassay with the inherent advantages of being high throughput, real time, and label free, but its sensitivity needs essential improvement for practical applications. Here, we report a dual signal amplification strategy using functional gold nanoparticles (AuNPs) followed by on-chip atom transfer radical polymerization (ATRP) for sensitive SPRi immunoassay of tumor biomarker in human serum. The AuNPs are grafted with an initiator of ATRP as well as a recognition antibody, where the antibody directs the specific binding of functional AuNPs onto the SPRi sensing surface to form immunocomplexes for first signal amplification and the initiator allows for on-chip ATRP of 2-hydroxyethyl methacrylate (HEMA) from the AuNPs to further enhance the SPRi signal. High sensitivity and broad dynamic range are achieved with this dual signal amplification strategy for detection of a model tumor marker, α-fetoprotein (AFP), in 10% human serum., (Copyright © 2014 Elsevier Inc. All rights reserved.)

A simple, eco-friendly method for the synthesis of gold nanoflowers using a non-proteinogenic amino acid is discussed in the present work. Gold nanostructure with unique morphology was synthesized, with the assistance of ornithine amino acid. Ornithine-stabilised gold nanoflowers were found to be highly sensitive towards mercury ions (Hg2+) due to Au–Hg amalgamate formation. Due to amalgamate formation, an evolution in morphology of ornithine-stabilised gold nanoflowers happens which can be monitored by the red shift in surface plasmon resonance. Under optimum conditions, our sensor shows a dynamic response range with a detection limit of 6 nM. This developed nanosensor can be used as Hg2+ ion sensor in polluted water/waste water by a one-step assay protocol. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (Au NPs) exhibit a localised surface plasmon resonance (LSPR) which can be excited in the visible spectral range and is sensitive to the size, shape and environment of the NP. Here, we present electronic action spectra of single 38.5–52.5 nm diameter Au NPs in the gas phase measured by means of single nanoparticle action spectroscopy at cryogenic temperatures (cryo-SNAS). A single Au NP is trapped in a temperature-controllable Paul-type ion trap, thermalised by collisions with a buffer gas and coated with messenger molecules at sufficiently low temperature, while its absolute mass is non-destructively monitored. Absorption of monochromatic electromagnetic radiation (400–800 nm) is detected indirectly by monitoring the change in mass due to messenger desorption. We find that the LSPR is red-shifted by ∼ 75 nm compared to the predicted value for a bare Au NP in vacuum. Laser heating changes the intensity, but not position or width of the LSPR and can be used to ultimately quench the LSPR. The measured spectra are modelled using Mie theory and assuming the formation and annealing of a refractive surface layer. [ABSTRACT FROM AUTHOR]

Tow-dimensional and 3-dimensional colloidal structures have been used to study surface-enhanced Raman scattering and localized surface plasmon resonance because of their regular stacking structures. However, freely controlling the number and size of the colloidal assemblies remains a challenge. In this study, we demonstrated the fabrication and mechanism of tiny nanoclusters using spontaneous evaporation-based nanofountain pens (NFPs). A micrometer-scale NFP nozzle was fabricated using a glass capillary. The gold nanoparticles (AuNPs) dispersed ink formed the pendant droplet at the NFP nozzle tip, where the AuNPs accumulated within the pendant droplet because of evaporation. The accumulated AuNPs were transferred onto the substrate via a stamp-like process to create nanoclusters. Using water evaporation analyzed by diffusion equations, we showed that reducing the AuNP accumulation to one hundred is possible. This precise adjustment enables fabrication until submicrometer-level nanoclusters. The fabrication method using NFPs can create 3D structures, and this operation is not significantly affected by the size or composition of the AuNPs. This could be expanded to metabolite-included nanocluster where metabolite can be located at the hot spot among AuNPs. Therefore, we expect that this will be utilized to create SERS signals and conduct disease diagnosis research using extremely small amounts of metabolites. [ABSTRACT FROM AUTHOR]

In the cosmeceutical industry, nanoparticles are becoming increasingly popular as carriers for drug delivery in a wide range of therapeutic applications. Incorporating curcumin into cosmetics formulation can transform them into a therapeutic products, as curcumin is an active compound with manu benefits. In order to advance dermatology research in cosmeceuticals, it is important to develop new ecologically friendly nanosized compounds for skin nanoparticulate systems. However, curcumin has low intrinsic activity, poor absorption, high metabolic rate, inactivity of metabolic products, and quick excretion and clearance from the body. These factors contribute to the lower bioavailability of the substance from reaching the target cells. Hence, this research aimed to optimise the preparation of curcumin-chitosan gold nanoparticles (CCG-NP) via UV-Vis surface plasmon resonance (SPR) band method by optimising the reaction ratio and time. The chitosan biocarrier was extracted from rhinoceros beetle, Oryctes rhinoceros. In this sttudy, the CCG-NPs were successfully synthesised at 70°C for 60 minutes under optimal conditions of reactant ratio of 2:0.5 (0.5 mM HAuCl4: 0.1 % curcumin). [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) can be described as nanozymes, species that are able to mimic the catalytic activities of several enzymes, such as oxidase/peroxidase, reductase, or catalase. Most studies in the literature focus on the colloidal suspension of AuNPs, and it is obvious that their immobilization could open the doors to new applications thanks to their increased stability in this state. This work aimed to investigate the behavior of surfaces covered by immobilized AuNPs (iAuNPs). Citrate-stabilized AuNPs (AuNPs-cit) were synthesized and immobilized on glass slides using a simple dip coating method. The resulting iAuNPs were characterized (surface plasmon resonance, microscopy, quantification of immobilized AuNPs), and their multi-enzymatic-like activities (oxidase-, peroxidase-, and catalase-like activity) were evaluated. The comparison of their activities versus AuNPs-cit highlighted their added value, especially the preservation of their activity in some reaction media, and their ease of reuse. The huge potential of iAuNPs for heterogeneous catalysis was then applied to the degradation of two model molecules of hospital pollutants: metronidazole and methylene blue. [ABSTRACT FROM AUTHOR]

A label-free impedimetric aptasensor for bisphenol A (BPA) was developed based on a novel method. Initially, gold nanoparticle-based nanoplatforms were prepared using a 4-mercaptophenyl (4MP) electrochemical nanofilm. Then, the BPA-selective aptamer (antiBPA) was immobilized on this platform for the sensitive and selective detection of BPA. The characterizations of the electrode preparation steps were performed using a transmission electron microscope, X-ray photoelectron spectroscopy, electrochemical methods, and atomic force microscopy. The aptamer immobilization concentration, immobilization time, and incubation time of BPA were optimized to get the best sensor response. The calibration curve exhibited good linearity between 10 fM and 10 nM with a correlation coefficient of 0.9963 and a limit of detection and limit of quantification values of 8.6 and 25.8 fM (S/N = 3), respectively. The developed aptasensor showed good reproducibility (RSD 2.55%), high sensitivity, specificity, and stability. The developed sensor was validated using real samples of tap water, lake water, and wastewater demonstrating promising performance. [ABSTRACT FROM AUTHOR]

This paper demonstrated the fabrication of an electrochemical-based aptasensor for the specific detection of the stress hormone "Cortisol" in Saliva. Gold nanoparticles have been widely explored as an immobilization substrate for the aptamer due to the direct covalent attachment through thiol bonding. Here, cortisol-specific truncated 14-mer aptamer was immobilized onto the gold nanoparticles-decorated screen-printed electrodes. The aptasensor has a broad dynamic range of 0.1 pg/ml–100 ng/ml with a detection limit of 0.25 pg/ml in buffer and 0.28 pg/ml in artificial saliva matrix. The sensitivity of the sensor was 1.53 µA (pg/ml)−1 in the buffer and 1.33 µA (pg/ml)−1 in the artificial saliva matrix. The proposed aptasensor has demonstrated high specificity towards cortisol and showed no change in the current signal towards the structural analogues of the cortisol. [ABSTRACT FROM AUTHOR]

Artificial nanozymes that are based on ferric oxides have drawn enormous attention due to their high stability, high efficiency, and low cost as compared with natural enzymes. Due to the unique optical plasmonic properties, gold nanoparticles (Au NPs) have been widely utilized in the fields of colorimetric, Raman, and fluorescence sensing. In this work, a photo-responsive Au@Fe3O4 nanozyme is prepared with outstanding peroxidase-like activity. The hot electrons of Au NPs that are excited by a surface plasmon resonance (SPR) effect of NPs improve the catalytic activity of Au@Fe3O4 in oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) and the detection of hydroquinone (HQ). The magnetic separation and reusability of the nanozyme further lower its costs. The detection linear range of the sensor is 0–30 μM and the lowest detection limit is 0.29 μM. Especially in the detection of real water samples, a good recovery rate is obtained, which provides promising references for the development of the HQ detection technology in seawater. [ABSTRACT FROM AUTHOR]

Gold nanoparticle (GNP) was prepared in situ using poly(ethylenimine)/(phenylthio) acetic acid(PEI/PTA) ion pair self-assembly(IPSAM) as a reducing and a capping material. The upper critical solution temperature of the ion pair was affected by the addition of gold ions. Gold ion could be converted to GNP in the IPSAM suspension by aging for 60–150 min. The aging period was shorter and the surface plasmon resonance signal of GNP was stronger as the ion concentration (0.5 and 2.5 mM) and the temperature (20, 30, and 40 °C) were higher. X-ray photoelectron spectroscopy revealed that gold existed with the PEI/PTA IPSAM as a metallic state after 24 h aging. A transmission electron microscopy revealed that GNP existed on the inside of the IPSAM and the lattice spacing of GNP was about 0.20 nm. The release degree of nile red loaded in the IPSAM under near-infrared (NIR) irradiation was proportional to the GNP content. The maximum release degree for 60 min was about 5.7, 6.5, 17.6, 32.4, and 41.2%, respectively, when the GNP content was 0, 0.25, 0.35, 0.6, and 1.55%. The IPSAM containing GNP would be used as a drug carrier that releases its cargo in answering to NIR irradiation. [ABSTRACT FROM AUTHOR]

Water resources of our earth is currently facing a serious challenge due to human activities including industrial development, agricultural revolution, urban growth and deforestation. The first step for pollutant removal is obviously their detection in water which requires use of various well known instrumentation techniques or use of sensors. Of all the different types of sensors, gold and silver nanoparticle based colorimetric/plasmonic nano-sensors are particularly noteworthy because of their simplicity and low cost. These nano-sensors are based on principle of SPR, an optical phenomenon immensely dependent on characteristics of the nanoparticles. Noble metal nanoparticles are widely chosen for colorimetric sensing application as their SPR absorbance lie in the visible region of spectrum rendering unique colors to them. Also, they are easy to synthesize, easy to functionalize, biocompatible and stable. In this detection technique, the presence of a pollutant is revealed by a distinct, visual color change and can also be quantified using a UV-Visible Spectrophotometer. Sustainable chemistry being one of the focal points of modern chemistry research, green synthesis of nanoparticles, particularly noble metal nanoparticles such as gold and silver have attracted considerable attention in last decade. Although gold and silver nanoparticles based optical sensor have been summarized in various reviews over last few years, colorimetric nano-sensors synthesized by green methods have found little discussion in scientific literature. This critical review aims to connect this gap by portraying this sparsely explored area of application of biosynthesized silver and gold nanoparticles and thus will assist the researchers working in this field. Green synthesis of silver and gold nanoparticles Colorimetric detection of environmental pollutants Metal mediated aggregation Redox etching Selectivity, sensitivity and Limit of Detection [ABSTRACT FROM AUTHOR]

The incidence of Mycobacterium tuberculosis (MTB) is increasing due to lack of appropriate diagnostic and therapeutic methods. Therefore, early and accurate detection of this bacteria plays a significant role in controlling tuberculosis. This study aimed to design, develop, and implement a direct and rapid detection method of MTB using modified gold nanoparticle (AuNP) colorimetric probe-based biosensor in sputum specimens. Spherical AuNPs were synthesized by the citrate reduction method and were functionalized using thiol-modified oligonucleotides (AuNP-biosensor). AuNP-biosensor and IS6110 PCR were compared to the gold standard in terms of analytical and clinical sensitivity and specificity, positive predictive value (PPV), negative predictive value (NPV), diagnostic odds ratio (DOR), and accuracy in 52 clinical specimens. Gold standard was defined as a positive result in concentrated sputum smear microscopy (SSM), culture, or Xpert MTB/RIF. The AuNP-biosensor had 100% sensitivity and specificity for detection of total sputum DNA in less than 15 min with ready-to-use AuNP-biosensor. PPV, NPV, DOR and accuracy of this method were 100%, 100%, 2325 and 100%, respectively. Considering the promising results of the diagnostic value indices of the AuNP-biosensor, the designed method is an affordable, rapid, reliable, and cost-beneficial way for direct detection of MTB in sputum specimens. [ABSTRACT FROM AUTHOR]

Rapid, sensitive, and reliable detection of high mobility group box 1 (HMGB1) is essential for medical and diagnostic applications due to its important role as a biomarker of chronic inflammation. Here, we report a facile method for the detection of HMGB1 using carboxymethyl dextran (CM-dextran) as a bridge molecule modified on the surface of gold nanoparticles combined with a fiber optic localized surface plasmon resonance (FOLSPR) biosensor. Under optimal conditions, the results showed that the FOLSPR sensor detected HMGB1 with a wide linear range (10−10 to 10−6 g/mL), fast response (less than 10 min), and a low detection limit of 43.4 pg/mL (1.7 pM) and high correlation coefficient values (>0.9928). Furthermore, the accurate quantification and reliable validation of kinetic binding events measured by the currently working biosensors are comparable to surface plasmon resonance sensing systems, providing new insights into direct biomarker detection for clinical applications. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) is a very sensitive measure of biomolecular interactions but is generally too expensive for routine analysis of clinical samples. Here we demonstrate the simplified formation of virus-detecting gold nanoparticle (AuNP) assemblies on glass using only aqueous buffers at room temperature. The AuNP assembled on silanized glass and displayed a distinctive absorbance peak due to the localized SPR (LSPR) response of the AuNPs. Next, assembly of a protein engineering scaffold was followed using LSPR and a sensitive neutron reflectometry approach, which measured the formation and structure of the biological layer on the spherical AuNP. Finally, the assembly and function of an artificial flu sensor layer consisting of an in vitro-selected single-chain antibody (scFv)-membrane protein fusion was followed using the LSPR response of AuNPs within glass capillaries. In vitro selection avoids the need for separate animal-derived antibodies and allows for the rapid production of low-cost sensor proteins. This work demonstrates a simple approach to forming oriented arrays of protein sensors on nanostructured surfaces that uses (i) an easily assembled AuNP silane layer, (ii) self-assembly of an oriented protein layer on AuNPs, and (iii) simple highly specific artificial receptor proteins. [ABSTRACT FROM AUTHOR]

A novel localized surface plasmon resonance (LSPR) system based on the coupling of gold nanomushrooms (AuNMs) and gold nanoparticles (AuNPs) is developed to enable a significant plasmonic resonant shift. The AuNP size, surface chemistry, and concentration are characterized to maximize the LSPR effect. A 31 nm redshift is achieved when the AuNMs are saturated by the AuNPs. This giant redshift also increases the full width of the spectrum and is explained by the 3D finite‐difference time‐domain (FDTD) calculation. In addition, this LSPR substrate is packaged in a microfluidic cell and integrated with a CRISPR‐Cas13a RNA detection assay for the detection of the SARS‐CoV‐2 RNA targets. Once activated by the target, the AuNPs are cleaved from linker probes and randomly deposited on the AuNM substrate, demonstrating a large redshift. The novel LSPR chip using AuNP as an indicator is simple, specific, isothermal, and label‐free; and thus, provides a new opportunity to achieve the next generation multiplexing and sensitive molecular diagnostic system. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) were synthesized using citrate reduction, also known as the Turkevich method. The AuNPs were compared with the commercially available product and later subjected to characterization. The AuNPs were 13 nm in diameter with a 2.7 × 108 M−1cm−1 extension coefficient. The calculated concentration was 5.1 nM through the Beer–Lambert law using UV–vis absorbance spectra. Further detailed characterization was applied, such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), elemental analysis using electro and DLS instruments, energy-dispersive X-ray spectroscopy (EDS), XRD, and Zeta potential. The synthesized AuNPs had a higher UV-absorbance peak of 0.93 in comparison to commercially available nanoparticles at 5.8 identical conditions. The characterization confirmed successful fabrication of colloidal-citrate-capped AuNPs and their dispersed and aggregated state with induced salt concentration. The shape and morphology were confirmed through XRD, showing a face-centered cubic lattice of {111}, confirmed at 38.1 round shape, and a crystalline lattice. AuNPs tend to be applied in sensing, detection, drug delivery, pharmaceuticals, and other applications in the environment and materials. Other applications include environmental contaminant detection, colorimetric sensors, antimicrobial applications, biosensing and drug delivery, tissue engineering, nanomedicines, optoelectronics, and catalysts. [ABSTRACT FROM AUTHOR]

Cancer ranks as a leading cause of death and a huge obstacle to rising life expectancy. If cancers are spotted early there's a high chance of survival. The conventional methods relying on the phenotypic features of the tumor are not powerful to the early screening of cancer. Cancer biomarkers are capable of indicating specific cancer states. Current biochemical assay suffers from time and reagents consuming and discontinuous monitoring. Surface plasmon resonance (SPR) technology, a refractive index-based optical biosensor, has significant promise in biomarker detection because of its outstanding features of label-free, sensitivity, and reliability. The nanomaterial features exotic physical and chemical property work on the process of transferring biorecognition event into SPR signal and hence is functioned as signal enhancer. In this review, we mainly discussed the mechanism of gold nanoparticles (AuNPs) and two-dimensional (2D) functional nanomaterial for improving the SPR signal. We also introduced AuNPs and 2D nanomaterial assisted SPR technology in determining cancer biomarker. Last but not least, we discussed the challenges and outlooks of the aforementioned reformative SPR technology for cancer biomarker determination in the clinical trial. [ABSTRACT FROM AUTHOR]

The global pandemic of COVID-19 has created an unrivalled need for sensitive and rapid point-of-care testing (POCT) methods for the detection of infectious viruses. For the novel coronavirus SARS-CoV-2, the nucleocapsid protein (N-protein) is one of the most abundant structural proteins of the virus and it serves as a useful diagnostic marker for detection. Herein, we report a fiber optic particle plasmon resonance (FOPPR) biosensor which employed a single-stranded DNA (ssDNA) aptamer as the recognition element to detect the SARS-CoV-2 N-protein in 15 min with a limit of detection (LOD) of 2.8 nM, meeting the acceptable LOD of 106 copies/mL set by the WHO target product profile. The sensor chip is a microfluidic chip based on the balance between the gravitational potential and the capillary force to control fluid loading, thus enabling the power-free auto-flowing function. It also has a risk-free self-contained design to avoid the risk of the virus leaking into the environment. These findings demonstrate the potential for designing a low-cost and robust POCT device towards rapid antigen detection for early screening of SARS-CoV-2 and its related mutants. [ABSTRACT FROM AUTHOR]

Active targeting is a promising approach for the treatment of viral infections. In particular, site-specific formulations for the treatment of HIV infection may overcome challenges associated with current ARV regimens. In this study we explored active targeting by synthesizing a gold nanoparticle construct decorated with an anti-CD4 cyclic peptide. The aim was to demonstrate selectivity of the system for the CD4 receptor and to deliver the RNA payload into T-lymphocytes. Colloidal gold nanoparticles functionalized with N -succinimidyl 3-(2-pyridyldithio) propionate (SPDP) were formed by a one-pot synthesis method where thiol modified polyethyleneimine (PEI) was mixed with chloroauric acid. PEI-SPDP AuNPs (gold nanoparticles) were conjugated to an anti-CD4 peptide and loaded with RNA. We measured toxicity and uptake using TZM-bl and HeLa cells. Our findings show that the nanoparticles bind selectively to CD4 + cells. UVâ€"vis characterisation of the nanoparticles revealed a surface plasmon resonance (SPR) peak at 527 nm, corresponding to a 6 nm diameter. HRTEM of the complete nanoparticles visualised circular shaped particles with average diameter of ∼7 nm. The polydispersity index was calculated to be 0.08, indicating monodispersity of complete NPS in solution. Through the pyridine-2-thione assay each nanoparticle was calculated to carry 1.37 × 105 SPDP molecules available for peptide binding. Flow cytometry showed that 13.6% of TZM-bl cells, and 0.14% of HeLa cells retained fluorescence after an overnight incubation, an indication of system binding. No internal RNA delivery was demonstrated. Further work is required to improve internalization. [ABSTRACT FROM AUTHOR]

Artificial nanozymes that are based on ferric oxides have drawn enormous attention due to their high stability, high efficiency, and low cost as compared with natural enzymes. Due to the unique optical plasmonic properties, gold nanoparticles (Au NPs) have been widely utilized in the fields of colorimetric, Raman, and fluorescence sensing. In this work, a photo-responsive Au@Fe3O4 nanozyme is prepared with outstanding peroxidase-like activity. The hot electrons of Au NPs that are excited by a surface plasmon resonance (SPR) effect of NPs improve the catalytic activity of Au@Fe3O4 in oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) and the detection of hydroquinone (HQ). The magnetic separation and reusability of the nanozyme further lower its costs. The detection linear range of the sensor is 0–30 μM and the lowest detection limit is 0.29 μM. Especially in the detection of real water samples, a good recovery rate is obtained, which provides promising references for the development of the HQ detection technology in seawater.

Gold nanoparticles with different mean sizes were formed on antimony‐doped tin oxide nanocrystals by the temperature‐varied deposition‐precipitation method (Au/ATO NCs). Au/ATO NCs possess strong absorption in the near‐infrared region due to Drude excitation in addition to the localized surface plasmon resonance (LSPR) of AuNPs around 530 nm. Au/ATO NCs show thermally activated catalytic activity for the oxidation of cinnamyl alcohol to cinnamaldehyde by hydrogen peroxide. The catalytic activity increases with a decrease in the mean Au particle size (dAu) at 5.3 nm≤dAu≤8.2 nm. Light irradiation (λex >660 nm, ∼0.5 sun) of Au/ATO NCs increases the rate of reaction by more than twice with ∼95 % selectivity. Kinetic analyses indicated that the striking enhancement of the reaction stems from the rise in the temperature near the catalyst surface of ∼30 K due to the photothermal effect of the ATO NCs. [ABSTRACT FROM AUTHOR]

[Display omitted] Substantial advancements have been observed over the years in the research and development of Localized Surface Plasmon Resonance (LSPR). A variety of current and future applications involving anisotropic plasmonic nanoparticles include biosensors, photothermal therapies, photocatalysis, and various other fields. Amongst various other applications, plasmonic enhancements are deployed in Surface Enhanced Raman Spectroscopy (SERS) mediated bio-sensing, absorption spectroscopy based analyte quantification, and fluorescence spectroscopy-based biomolecular detection up to femtomolar level and even on the level of single molecules. LSPR based healthcare diagnostics and therapeutics have grown much faster than expected, with an increased number of published original research articles and reviews. Despite the extensive literature available, a comprehensive review with a focused emphasis on recent advances in the field of plasmonic particle anisotropy, plasmonic nanostructure, plasmonic coupling mediated enhanced LSPR intensity and their diverse applications in biosensing is needed. This article focuses on LSPR properties of anisotropic nanostructures like spherical gold nanoparticles (AuNP), gold nanorod (AuNR), gold nanostar (AuNs), gold nanorattles (AuNRT), gold nanoholes (AuNH), dimeric nanostructures and their role in plasmonic enhancements for targeted biosensing and therapeutic research. The contemporary state of the art biosensing development around SERS has also been discussed. A detailed literature analysis of recent development in micro-surgery, photothermal tumor killing, biosensor development for detection up to single molecule level, high-efficiency drug delivery are covered in this article. Furthermore, recent and advanced technologies including Spatially Offset Raman Spectroscopy (SORS), Surface Enhanced Resonance Raman Spectroscopy (SERRS), and Surface Enhanced Spatially Offset Raman Spectroscopy (SESORS) are presented citing their importance in biosensing. We complement this review article with relevant theoretical frameworks to understand finer nuances within the literature that is discussed. [ABSTRACT FROM AUTHOR]

Surface‐enhanced Raman spectroscopy (SERS) is a powerful tool for nondestructive and ultrasensitive optical trace‐detection. However, the sophisticated fabrication processes and performance degradation on flexible substrates block SERS for practical uses. Here, we report a facile flexible microsphere‐coupled SERS (McSERS) substrate composed of a dielectric microsphere cavity array (MCA) and random gold nanoparticles (AuNPs) capping on a polydimethylsiloxane (PDMS) film (MCA/AuNPs/PDMS) for giant Raman enhancement. The random distribution of AuNPs provides a hydrophilic surface against to the coffee‐ring effect for uniform localized surface plasmon resonance (LSPR) response. The MCA capped on the AuNPs boosts the Raman intensity via the multiple optical manipulation processes, in which the photonic nanojet (PNJ) confines the excitation intensity near the AuNPs, whispering‐gallery mode (WGM) facilitates the energy transfer from microsphere cavities to AuNP gaps for LSPR boosting, and directional antenna effect converts near‐field Raman signals into far‐field with a small divergence. Therefore, the Raman scattering is dramatically improved with the enhancement factor (EF) to 107 for the limit of detection (LoD) of 4‐nitrobenzenethiol (4‐NBT) molecules down to 0.1 nM, two orders of magnitude higher via MCA coupling. Moreover, the flexible McSERS substrate exhibits outstanding durability and compatibility as an ultrasensitive Raman test strip, by which the thiram concentration is detectable down to 2.42 ng/cm2 on apple peels. The present work provides a facile strategy to fabricate SERS substrates with high flexibility for optical trace‐detection in real‐world applications. [ABSTRACT FROM AUTHOR]

This study develops a highly sensitive and low-cost carboxyl-graphene-oxide-based planar optical waveguide localized surface plasmon resonance biosensor (GO-OW LSPR biosensor), a system based on measuring light intensity changes. The structure of the sensing chip comprises an optical waveguide (OW)-slide glass and microfluidic-poly (methyl methacrylate) (PMMA) substrate, and the OW-slide glass surface-modified gold nanoparticle (AuNP) combined with graphene oxide (GO). As the GO has an abundant carboxyl group (–COOH), the number of capture molecules can be increased. The refractive index sensing system uses silver-coated reflective film to compare the refractive index sensitivity of the GO-OW LSPR biosensor to increase the refractive index sensitivity. The result shows that the signal variation of the system with the silver-coated reflective film is 1.57 times that of the system without the silver-coated reflective film. The refractive index sensitivity is 5.48 RIU−1 and the sensor resolution is 2.52 ± 0.23 × 10−6 RIU. The biochemical sensing experiment performs immunoglobulin G (IgG) and streptavidin detection. The limits of detection of the sensor for IgG and streptavidin are calculated to be 23.41 ± 1.54 pg/mL and 5.18 ± 0.50 pg/mL, respectively. The coefficient of variation (CV) of the repeatability experiment (sample numbers = 3) is smaller than 10.6%. In addition, the affinity constants of the sensor for anti-IgG/IgG and biotin/streptavidin are estimated to be 1.06 × 107 M−1 and 7.30 × 109 M−1, respectively. The result shows that the GO-OW LSPR biosensor has good repeatability and very low detection sensitivity. It can be used for detecting low concentrations or small biomolecules in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • PC@GF-aptasensor was based on the plasmonic colorimetry and G4 fluorescence. • Dual-mode, antibody-free, enzyme-free and label-free system was displayed. • Three readouts: naked-eye, smartphone and spectrofluorometer. • The reliability, practicability and selectivity were well improved. • New approach for improving the performance of aptasensor might provide. G-quadruplexes (G4) have received significant attention in the field of aptasensors owing to their unique physicochemical characteristics. A dual-mode, protein-free and label-free aptamer sensor based on plasmonic colorimetry and G4 fluorescence (PC@GF-aptasensor) was proposed for ochratoxin A (OTA). Colorimetry mode was achieved through the surface plasmon resonance (SPR) effect, which related to the OTA-Apt-based G4–OTA. The fluorescence mode was reflected by the insertion of thioflavin T (ThT) into G4–OTA. The OTA could be interpreted via three readouts: (1) naked eye (LOD of 2.0 ng mL−1), (2) smartphone (LOD of 1.65 ng mL−1), and (3) spectrofluorometer (LOD of 0.93 ng mL−1). The PC@GF-aptasensor exhibited several advantages, such as a standardised recognition group, simplified operation, low background signal, and practicality. The proposed PC@GF-aptasensor integrated SPR-based multicolour interpretation and ThT-inserted fluorescence reflection to obtain a dual-mode optical biosensor, which may provide valuable insights for the development of other targets with G4-based aptamers. [ABSTRACT FROM AUTHOR]

Mortality level is worsening the situation worldwide thru blood diseases and greatly jeopardizes the human health with poor diagnostics. Due to the lack of successful generation of early diagnosis, the survival rate is currently lower. To overcome the present hurdle, new diagnostic methods have been choreographed for blood disease biomarkers analyses with the conjunction of ultra-small ideal gold nanohybrids. Gold-hybrids hold varieties of unique features, such as high biocompatibility, increased surface-to-volume ratio, less-toxicity, ease in electron transfer and have a greater localized surface plasmon resonance. Gold-nanocomposites can be physically hybrid on the sensor surface and functionalize with the biomolecules using appropriate chemical conjugations. Revolutionizing biosensor platform can be prominently linked for the nanocomposite applications in the current research on medical diagnosis. This review encloses the new developments in diagnosing blood biomarkers by utilizing the gold-nanohybrids. Further, the current state-of-the-art and the future envision with digital monitoring for facile telediagnosis were narrated. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) show unique size‐ and shape‐dependent photosensitive properties resulting from localized surface plasmon resonance, which can be exploited in colorimetric sensors. Polyamidoamine (PAMAM) dendrimers are suitable nanotemplates of AuNPs and nanoplatforms of some stimuli‐responsive materials. In this study, AuNP was loaded in phenylalanine (Phe)‐modified PAMAM dendrimers with dual pH‐ and temperature‐sensitive properties to produce a naked‐eye colorimetric sensor with responsivity to both pH and temperature. The ultraviolet‐visible (UV‐Vis) spectra of AuNP‐loaded PAMAM‐Phe‐Suc were changed by heating at pH 4 and 5, but unchanged at pH above 5.5. The UV‐Vis spectra of AuNP‐loaded PAMAM‐Phe and PAMAM‐Suc were only slightly changed by heating at pH above 5.5 and at pH 4 and 5, respectively. In solution, AuNP‐loaded PAMAM‐Phe‐Suc changed color (from brown to gray) under high temperature (≥50 °C) and acidic (pH≤5) conditions, suggesting its functionality as a naked‐eye colorimetric dual pH and temperature sensor. [ABSTRACT FROM AUTHOR]

Viruses are infectious agents that pose significant threats to plants, animals, and humans. The current coronavirus disease 2019 pandemic, which is caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), has spread globally and resulted in over 2 million deaths and immeasurable financial losses. Rapid and sensitive virus diagnostics become crucially important in controlling the spread of a pandemic before effective treatment and vaccines are available. Gold nanoparticle (AuNP)‐based testing holds great potential for this urgent unmet biomedical need. In this review, we describe the most recent advances in AuNP‐based viral detection applications. In addition, we discuss considerations for the design of AuNP‐based SARS‐CoV‐2 testings. Finally, we highlight and propose important parameters to consider for the future development of effective AuNP‐based testings that would be critical for not only this COVID‐19 pandemic, but also potential future outbreaks. This article is categorized under:Diagnostic Tools > BiosensingDiagnostic Tools > In Vitro Nanoparticle‐Based Sensing [ABSTRACT FROM AUTHOR]

This study explores the feasibility of enhancing the water splitting performance of hybrid photo‐electrocatalyst made from graphene quantum dots (GQDs) grafted with gold nanoparticles (Au NPs) deposited on crystal facet engineered TiO2 (Ti). The effect of the Au NPs size on photoelectrochemical (PEC) water splitting performance was systematically investigated. It was found that the TiO2 with co‐exposed {001}‐{010} facet deposited with large particle size of Au NPs showed an enhancement in PEC performance, due to the localized surface plasmon resonance (LSPR). By contrast, the system containing Au NPs with smaller size retarded the transport rate of free electrons because of their high electron affinity. Interestingly, the hybrid catalyst (GQDs‐Aud40/Ti) delivered a considerable high current density (0.535 mA/cm2 at 1.23 V vs RHE), as compared to the pristine TiO2 (0.267 mA/cm2). This was due to the capability of GQDs in acting as an electron extractor, withdrawing hot electrons produced by Au NPs and inhibiting the charge recombination. Overall, this work demonstrated that the PEC water splitting performance of TiO2 based photo‐electrocatalyst can be synergistically enhanced by combining the plasmonic effect of Au NPs and electron extractor properties of GQDs. [ABSTRACT FROM AUTHOR]

Circulating cell-free DNA (cfDNA) is known to be an attractive biomarker for liquid biopsy. In this work, a rapid and sensitive biosensor was achieved for cfDNA detection based on CRISPR-associated nuclease 12a (CRISPR-Cas12a) and single nanoparticle dark-field microscopy (DFM) imaging. The biosensor employed gold nanoparticles (AuNPs) as signal source, DFM as readout system, and Meanshift algorithms as the image processing systems, respectively. The presence or absence of cfDNA caused the different existing states (monomer or aggregated state) of AuNPs. AuNPs monomers could be effectively distinguished from the aggregated ones under DFM since the AuNPs aggregation could induced the green-to-yellow or green-to-red changing of scattering color. The monomer ratio easily obtained by Meanshift and partial least-square (PLS) algorithms was used for quantitative analysis. Using this strategy, breast cancer gene-1 (BRCA-1), a representative of cfDNA biomarker for breast cancer could be measured with high sensitivity in 40 min and has a low detection limit of 0.081 fM. It is hoped that this nucleic acid amplification-free sensor could be also utilized to detect other nucleic acid biomarkers, and thus, provides a novel strategy for biomedical image analysis. [Display omitted] • A new biosensor was developed for rapid and sensitive cfDNA detection. • This is a biosensing strategy avoiding nucleic acid amplification. • CRISPR-Cas12a and single nanoparticle DFM imaging had been applied to increase the sensitivity. • The Meanshift and partial least-square (PLS) algorithms was used for quantitative analysis. • This biosensor had been used to detect the breast cancer gene-1 (BRCA-1) in cell lysates with satisfied performance. [ABSTRACT FROM AUTHOR]

Membrane proteins (MPs) are affected by binding of specific lipids. We previously developed a methodology for systematically analyzing MP-lipid interactions leveraging surface plasmon resonance (SPR). In this method, the gold sensor chip surface was modified with a self-assembled monolayer (SAM), which allowed for a larger amount of MP-immobilization. However, the laborious lipid purification step remained a bottleneck. To address this issue, a new strategy has been developed utilizing gold nanoparticles (AuNPs) instead of the gold sensor chip. AuNPs were coated with SAM, on which MP was covalently anchored. The MP-immobilized AuNPs were mixed with a lipid mixture, and the recovered lipids were quantified by LC–MS. Bacteriorhodopsin (bR) was used as an MP to demonstrate this concept. We optimized immobilization conditions and confirmed the efficient immobilization of bR by dynamic light scattering and electron micrographs. Washing conditions for pulldown experiments were optimized to efficiently remove non-specific lipids. A new binding index was introduced to qualitatively reproduce the known affinity of lipids for bR. Consequently, the low-abundant and least-studied lipid S-TeGD was identified as a candidate for bR-specific lipids. This technique can skip the laborious lipid purification process, accelerating the screening of MP-specific lipids from complex lipid mixtures. [Display omitted] • The actions of membrane proteins (MPs) are influenced by specific membrane lipids. • We previously developed a SPR-based method for analyzing MP-lipid interactions. • Extending this method, we developed a new technique employing Au nanoparticles. • A new binding index was introduced to identify MP-specific lipids from lipid mixtures. • A minor lipid was identified as a candidate for specific lipids of bacteriorhodopsin. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two haptens of tebufenozide with excellent immunologic effect were synthesized. • Sensitive and specific anti-tebufenozide monoclonal antibodies were prepared. • LFIA was developed and its sensitivity met MRLs of tebufenozide in agro-products. • Accuracy and reliability of LFIA were proved by UPLC-MS/MS validation. Tebufenozide is a non-steroidal insect growth regulator, which has been widely used in agriculture to control pests. Despite being recognized as an eco-friendly pesticide, its residues still can pose potential health hazards to humans. In this study, two haptens of tebufenozide were synthesized to prepare the monoclonal antibodies (mAbs). Out of the eight mAbs, mAb 5C5B6 exhibited the highest sensitivity (half maximal inhibitory concentration = 0.15 ng/mL) in the heterologous indirect competitive enzyme-linked immunosorbent assay, and was utilized to develop gold nanoparticle lateral flow immunoassay (LFIA). The cut-off value and visual limit of detection of the LFIA were 10 and 1.25 ng/mL. The detection results of both the spiked and blind samples demonstrated that the proposed LFIA exhibits high accuracy in detecting tebufenozide in agricultural products. [ABSTRACT FROM AUTHOR]