Highly sensitive visual detection of amantadine residues in poultry at the ppb level: A colorimetric immunoassay based on a Fenton reaction and gold nanoparticles aggregation

Photoelectrochemical sensors based on paper and their emerging applications in point-of-care testing

Point-of-care testing (POCT) technology is urgently required owing to the prevalence of the Internet of Things and portable electronics. In light of the attractive properties of low background and high sensitivity caused by the complete separation of excitation source and detection signal, the paper-based photoelectrochemical (PEC) sensors, featured with fast in analysis, disposable and environmental-friendly have become one of the most promising strategies in POCT. Therefore, in this review, the latest advances and principal issues in the design and fabrication of portable paper-based PEC sensors for POCT are systematically discussed. Primarily, the flexible electronic devices that can be constructed by paper and the reasons why they can be used in PEC sensors are expounded. Afterwards, the photosensitive materials involved in paper-based PEC sensor and the signal amplification strategies are emphatically introduced. Subsequently, the application of paper-based PEC sensors in medical diagnosis, environmental monitoring and food safety are further discussed. Finally, the main opportunities and challenges of paper-based PEC sensing platforms for POCT are briefly summarized. It provides a distinct perspective for researchers to construct paper-based PEC sensors with portable and cost-effective, hoping to enlighten the fast development of POCT soon after, as well as benefit human society.

Robust Rules for Optimal Colorimetric Sensing Based on Gold Nanoparticle Aggregation

Spurred by outstanding optical properties, chemical stability, and facile bioconjugation, plasmonic metals have become the first-choice materials for optical signal transducers in biosensing. While the design rules for surface-based plasmonic sensors are well-established and commercialized, there is limited knowledge of the design of sensors based on nanoparticle aggregation. The reason is the lack of control over the interparticle distances, number of nanoparticles per cluster, or multiple mutual orientations during aggregation events, blurring the threshold between positive and negative readout. Here we identify the geometrical parameters (size, shape, and interparticle distance) that allow for maximizing the color difference upon nanoparticle clustering. Finding the optimal structural parameters will provide a fast and reliable means of readout, including unaided eye inspection or computer vision.

Gold Nanoparticle-Based Plasmonic Biosensors

One of the emerging technologies in molecular diagnostics of the last two decades is the use of gold nanoparticles (AuNPs) for biosensors. AuNPs can be functionalized with various biomolecules, such as nucleic acids or antibodies, to recognize and bind to specific targets. AuNPs present unique optical properties, such as their distinctive plasmonic band, which confers a bright-red color to AuNP solutions, and their extremely high extinction coefficient, which makes AuNPs detectable by the naked eye even at low concentrations. Ingenious molecular mechanisms triggered by the presence of a target analyte can change the colloidal status of AuNPs from dispersed to aggregated, with a subsequent visible change in color of the solution due to the loss of the characteristic plasmonic band. This review describes how the optical properties of AuNPs have been exploited for the design of plasmonic biosensors that only require the simple mixing of reagents combined with a visual readout and focuses on the molecular mechanisms involved. This review illustrates selected examples of AuNP-based plasmonic biosensors and promising approaches for the point-of-care testing of various analytes, spanning from the viral RNA of SARS-CoV-2 to the molecules that give distinctive flavor and color to aged whisky.

Comparison of LC-MS3 and LC-MRM Methods for Quantifying Amantadine and Its Application in Therapeutic Amantadine Monitoring in Human Plasma

A simple sample preprocessing method was developed for the quantitative determination of amantadine (AMT) in human plasma by liquid chromatography-tandem mass spectrometry cubed (LC-MS3). The LC-MS3 system comprised a Shimadzu Exion LC-20AD HPLC pump coupled with a QTRAP 5500 mass spectrometer. First, the plasma samples were pretreated using acetonitrile as the extracting solution to precipitate protein. Next, amantadine and amantadine-d15 (AMT-d15) were separated on an Agilent Poroshell 120 SB-C18 column (4.6 mm × 50 mm, 2.7 μm) using isocratic elution with solvent A (70% 0.1% formic acid) and solvent B (30% acetonitrile) at a flow rate of 0.8 mL/min. The total run time for each sample was 3 min. The system used triple-stage fragmentation transitions at m/z 152.2→135.3→107.4 for AMT quantification in the positive ion mode and m/z 167.0→150.3→118.1 for AMT-d15 quantification. The LC-MS3 assay was linear (r > 0.995) with a concentration range of 50−1500 ng/mL. The lower limit of quantification (LLOQ) was 50 ng/mL, and the intra-day and inter-day accuracies and precisions were less than 8.0% at all concentrations. In addition, the recoveries and matrix effect for AMT in human plasma were within acceptable limits. In terms of stability, AMT had no significant degradation under all conditions. All the results met the requirements of the guidelines of the Food and Drug Administration (FDA) for biological method validation. The novelty of the MS3 assay was that it presented a methodology with higher selectivity and sensitivity. This method was successfully applied to 44 human plasma samples, and the obtained quantitative results were compared with another liquid chromatography-multiple reaction monitoring (LC-MRM) method. The Passing-Bablok regression coefficients and Bland-Altman plot revealed no difference between the LC-MS3 and LC-MRM methods, implying that the developed LC-MS3 method is a reliable and accurate assay for AMT determination in human plasma. These results are also a proof of concept for determining chemicals in biological samples by the LC-MS3 strategy.

Current perspective on veterinary drug and chemical residues in food of animal origin

The marked increase in the demand for animal protein of high quality necessitates protecting animals from infectious diseases. This requires increasing the use of veterinary therapeutics. The overuse and misuse of veterinary products can cause a risk to human health either as short-term or long-term health problems. However, the biggest problem is the emergence of resistant strains of bacteria or parasites. This is in addition to economic losses due to the discarding of polluted milk or condemnation of affected carcasses. This paper discusses three key points: possible sources of drug and chemical residues, human health problems, and the possible method of control and prevention of veterinary drug residues in animal products.

Effect of amines on formation of gold/polyurethane foam nanocomposites and its sensing opportunities

Effect of amines on formation of gold nanoparticles (AuNPs)/polymer nanocomposites has been observed and studied. Nanocomposites based on polyurethane foam and AuNPs were synthesized by interaction between the polymer modified with sodium borohydride and aqueous solution of tetrachloroauric acid. It has been shown that some amines cause a remarkable decrease of the surface plasmon resonance band of AuNPs in the nanocomposite material. Both aliphatic and aromatic amines as well as amines containing several amino groups were studied. A possible mechanism of the effect is discussed. It is probably based on stabilization of AuNPs with an amine that entails a decrease in the degree of their adsorption on PUF and appearance of the stabilized AuNPs in solution. The decrease of the nanocomposite surface plasmon resonance band is proportional to the concentration of amine in the solution. Based on this effect, a method for the determination of cetylamine, β-naphthylamine and neomycin in water and medical formulations using a monitor calibrator as a portable household tool is proposed. Under the selected conditions, the detection limits for amines were in the range of 0.7-1.5 μM, the determination ranges were approximately an order of magnitude. The observed color change of the nanocomposite samples also provides a good basis for semiquantitative determinations.

A Fenton-like reaction system with analyte-activated catfish effect as an enhanced colorimetric and photothermal dopamine bioassay

Fenton-like reaction systems have been proven to be efficient as powerful promoters in advanced oxidation processes (AOPs) due to their generated reactive oxygen species (ROS), such as ˙OH and ˙O₂^-, which can further oxidize a specific chromogenic substrate like 3,3',5,5'-tetramethylbenzidine (TMB) to generate sensitive color readout and thereby demonstrate more potential in the colorimetric analysis field. However, the inherent drawback of the low rate-limiting step of Fe³⁺/Fe²⁺ conversion in the Fenton-like reaction and its resultant inefficiency for H₂O₂ decomposition hinder its practical applications. We herein communicate an analyte-activated catfish effect based catalysis strategy to promote the Fenton-like reaction, in which dopamine, like a catfish, was added to activate the Fenton-like reaction. By definition, the conversion rate of Fe³⁺ to Fe²⁺ in the proposed Fenton-like reaction can be significantly accelerated through a specific DA-mediated electron transfer process which further promotes the reaction activity in the Fenton-like reaction to generate more ˙OH and ˙O₂^- radicals. As a result, the produced ˙OH and ˙O₂^- radicals in such a reaction system can significantly oxidize TMB indicator into its oxidation product (TMBox) and therefore indicate the corresponding target-dependent color and photothermal signal readout, enabling the successful fabrication of a more sensitive and stable colorimetric and photothermometric DA sensor. More significantly, this strategy can greatly advance the practical application of Fenton-like reactions in the fields of colorimetric and photothermometric bioassays.

Applications of gold nanoparticles in ELISA, PCR, and immuno-PCR assays: A review

Development of state-of-the-art assays for sensitive and specific detection of disease biomarkers has received significant interest for early detection and prevention of various diseases. Enzyme Linked Immunosorbent assays (ELISA) and Polymerase Chain Reaction (PCR) are two examples of proteins and nucleic acid detection assays respectively, which have been widely used for the sensitive detection of target analytes in biological fluids. Recently, immuno-PCR has emerged as a sensitive detection method, where high specificity of sandwich ELISA assays is combined with high sensitivity of PCR for trace detection of biomarkers. However, inherent disadvantages of immuno-PCR assays limit their application as rapid and sensitive detection method in clinical settings. With advances in nanomaterials, nanoparticles-based immunoassays have been widely used to improve the sensitivity and simplicity of traditional immunoassays. Owing to facile synthesis, surface functionalization, and superior optical and electronic properties, gold nanoparticles have been at the forefront of sensing and detection technologies and have been extensively studied to improve the efficacies of immunoassays. This review provides a brief history of immuno-PCR assays and specifically focuses on the role of gold nanoparticles to improve the sensitivity and specificity of ELISA, PCR and immuno-PCR assays.

Development of homogeneous plasmonic potency assay using gold nanoparticle immunocomplexes

We evaluated the use of gold nanoparticles (AuNPs) platform in a homogenous assay for a potency measurement of a therapeutic monoclonal antibody (mAb). The recombinant human ligand protein to the therapeutic mAb was immobilized on AuNPs via functionalized self-assembled monolayers. Binding of the mAb to ligand lead to plasmonic signals that were detected faster in a homogeneous assay than the conventional enzyme-linked immunosorbent assay (ELISA). In this study, we demonstrated that the AuNP-based homogeneous plasmonic immunoassay (HPI) generated comparable potency values of a therapeutic mAb to a conventional binding ELISA in relatively shorter assay time and steps. Binding HPI can be potentially implemented as a potency assay for therapeutic mAbs in quality control laboratories.

Site-directed mutations of anti-amantadine scFv antibody by molecular dynamics simulation: prediction and validation

A recombinant single-chain variable fragment (scFv) antibody was produced from a hybridoma cell strain secreting the monoclonal antibody for amantadine (AMD), and then its recognition mechanisms for AMD were studied using the molecular docking and molecular dynamics. Complex dockings revealed that three regions are involved in antibody recognition; framework 2 of the VL chain (LFR2) GLU40 and TYR42, complementarity-determining region of the VL chain (LCDR3) TYR116, and framework 2 of the VH chain (HFR2) HIS40 and TRP52 were the key amino acid residues. The results of molecular dynamics show that the most important amino acid residues in the interaction between AMD and scFv are HIS40 and TYR116. On the basis of the results of virtual mutation, the scFv antibody was evolved by directional mutagenesis of amino acid residue GLY107 to PHE. Indirect competitive ELISA (icELISA) results indicated that the scFv mutant had highly increased affinity for AMD with up to 3.9-fold improved sensitivity. Thus, the scFv antibody can be applied for mechanistic studies of intermolecular interactions, and our work offered affinity maturated antibodies by site mutations, which were beneficial for valuable anti-AMD antibody design and preparation in future.

Ratiometric fluorescent sensing system for drug residue analysis: Highly sensitive immunosensor using dual-emission quantum dots hybrid and compact smartphone based-device

Immunoassays such as the enzyme-linked immunosorbent assay (ELISA) are utilized extensively for detecting protein biomarkers and small molecules in healthcare, environmental monitoring, and food analysis. Unfortunately, the current strategies for immunoassays often require sophisticated apparatus such as a microplate reader, which might not be available in resource-limited areas. To mitigate this problem, we designed a compact smartphone based-device and a multicolor response immunosensor. First, we designed a compact and cost-effective 3D-printed attachment, where a light-emitting diode was used as a light excitation source and a smartphone captured the fluorescent emission signals. Second, by combining quantum dots hybrid and chemical redox reaction, multiple color responses were displayed in the presence of the analyte at different concentrations. Third, solutions with distinct tonality could be readily distinguished by the naked eye and they were suitable for quantitative analysis using the hue-saturation-lightness color space based on a smartphone application. The versatility of the proposed sensing system was demonstrated by implementing an indirect competitive ELISA for analyzing trace drug residues in foodstuffs. The multicolor response of this sensing strategy allows us to visually quantify drug residues in foodstuffs. Moreover, the smartphone-based immunosensor can assess the exact concentration of the analyte by using a self-designed mobile application. The proposed assay provides a highly sensitive performance that the limit of detection was 0.37 ng/mL by visual detection and 0.057 ng/mL using the compact device. Due to its advantages in terms of portability, straightforward visual detection, high sensitivity, and cost effectiveness, the proposed immunosensor has great potential for applications in areas without access to laboratories or expensive infrastructure.

An Aggregation-Induced Emission-Based Indirect Competitive Immunoassay for Fluorescence "Turn-On" Detection of Drug Residues in Foodstuffs

A new fluorescent "turn-on" probe-based immunosensor for detecting drug residues in foodstuffs was established by combining the mechanism of aggregation-induced emission (AIE) and an indirect competitive enzyme-linked immunosorbent assay (ELISA). In this study, a luminogen, with negligible fluorescence emission (TPE-HPro), aggregated in the presence of H2O2, and exhibited astrong yellow emission based on its AIE characteristics. This AIE process was further configured into an immunoassay for analyzing drug residues in foodstuffs. In this approach, glucose oxidase (GOx) was used as an enzyme label for the immunoassay and triggered GOx/glucose-mediated H2O2 generation, which caused oxidation of TPE-HPro and a "turn-on" fluorescence response at 540 nm. To quantitatively analyze the drug residues in foodstuffs, we used amantadine (AMD) as an assay model. By combining the AIE-active "turn-on" fluorescent signal generation mechanism with conventional ELISAs, quantifying AMD concentrations in chicken muscle samples was realized with an IC50 (50% inhibitory concentration) value of 0.38 ng/mL in buffer and a limited detection of 0.06 μg/kg in chicken samples. Overall, the conceptual integration of AIE with ELISA represents a potent and sensitive strategy that broadens the applicability of the AIE-based fluorometric assays.

Nanomaterials-Based Colorimetric Immunoassays

Colorimetric immunoassays for tumor marker detection have attracted considerable attention due to their simplicity and high efficiency. With the achievements of nanotechnology and nanoscience, nanomaterials-based colorimetric immunoassays have been demonstrated to be promising alternatives to conventional colorimetric enzyme-linked immunoassays. This review is focused on the progress in colorimetric immunoassays with the signal amplification of nanomaterials, including nanomaterials-based artificial enzymes to catalyze the chromogenic reactions, analyte-induced aggregation or size/morphology change of nanomaterials, nanomaterials as the carriers for loading enzyme labels, and chromogenic reactions induced by the constituent elements released from nanomaterials.

Noble Metal Nanoparticles Applications: Recent Trends in Food Control

Scientific research in the nanomaterials field is constantly evolving, making it possible to develop new materials and above all to find new applications. Therefore, nanoparticles (NPs) are suitable for different applications: nanomedicine, drug delivery, sensors, optoelectronics and food control. This review explores the recent trend in food control of using noble metallic nanoparticles as determination tools. Two major uses of NPs in food control have been found: the determination of contaminants and bioactive compounds. Applications were found for the determination of mycotoxins, pesticides, drug residues, allergens, probable carcinogenic compounds, bacteria, amino acids, gluten and antioxidants. The new developed methods are competitive for their use in food control, demonstrated by their validation and application to real samples.