Nanozyme-Inhibited SERS Multichannel Paper-Based Sensor Array for the Quantification and Identification of Biothiols and Cancer Cells Based on Three Ag-Based Nanomaterials

Biothiols play essential roles in maintaining normal physiological functions, resisting oxidative stress, and protecting cell health. Establishing an effective and reliable sensor array for the accurate quantification and discrimination of diverse biothiols is extremely meaningful. In this work, Ag/Mn3O4, Ag3PO4, and Ag3Cit with excellent oxidase-mimetic activity and surface-enhanced Raman scattering (SERS)-enhanced features have been prepared and loaded onto Whatman filter paper (WFP) to build SERS paper chips as three sensing channels, which can induce 3,3',5,5'-tetramethylbenzidine (TMB) oxidation to SERS-active reporters (TMBox) and concurrently generate prominent SERS signals. Nevertheless, the addition of biothiols can suppress conversion from TMB to TMBox, which can cause the reduction of the SERS signal from TMBox. Interestingly, each SERS sensing channel can generate different TMBox signals' variations due to differences in the oxidative inhibition abilities of diverse biothiols and exclusive properties of each paper chip, which can be plotted as specific fingerprint patterns of each biothiol and further translated into intuitive two-dimensional (2D) clustering profiles through linear discriminant analysis (LDA) and hierarchical cluster analysis (HCA) techniques for precise identification of these six biothiols with the minimum concentration of 1 μM. More importantly, this SERS sensor array is exploited for the precise quantification of intracellular glutathione (GSH), and can differentiate between normal and cancer cells based on different intracellular GSH contents and even identify different types of tumor cells, demonstrating its powerful application prospects in disease diagnosis.

A smartphone-based colorimetric assay using Au@Ag core-shell nanoparticles as the nanoprobes for visual tracing of fluvoxamine in biofluids as a common suicide drug

In the present study, bimetallic nanoparticles (NPs) consisting of gold (AuNPs) as the core and silver (AgNPs) as the shell have been synthesized and applied as the nanoprobe for detection of fluvoxamine (FXM) as the anti-depression drug. The physicochemical properties of the prepared citrate-capped Au@Ag core-shell NPs have been characterized by UV-Vis, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) techniques. The design of the smartphone-based colorimetric FXM sensor relies on the fast hydrolysis of FXM under alkaline conditions by producing of 2-(Aminooxy)ethanamine without any significant peak at 400-700 nm. The interaction of the resulted molecule with the nanoprobe induced a red shift in the longitudinal localized surface plasmon resonance (LSPR) peak of the nanoprobe, which was accompanied by sharp and vivid color variations in the solution. A linear relationship between the absorption signal increasing by FXM concentration increasing from 1 µM to 10 µM presented a simple, low cost and minimally instrumented format for FXM quantification with a limit of detection (LOD) of 100 nM. The collected visual data with the elegant colorimetric response of the nanoprobe in the presence of FXM from Indian red to light red violet and bluish-purple color offered simple detection of FXM with the naked eye. The satisfactory results of the proposed cost-effective sensor in the rapid assay of FXM in human serum, urine, saliva and pharmaceutical samples guarantee the potential of the nanoprobe for on-site and visual determination of FXM in actual samples. The proposed sensor as the first non-invasive FXM sensor for saliva sample analysis may hold great promise to provide the technical support for the rapid and valid detection of FXM for forensic medicine and clinical organizations.

Cationic Polystyrene Resin Bound Silver Nanocomposites Assisted Fourier Transform Infrared Spectroscopy for Enhanced Catalytic Reduction of 4-Nitrophenol in Aqueous Medium

The present work reported a novel strategy to construct supported cationic-polystyrene-resin-bound silver nanocomposites for enhanced catalytic reduction of 4-nitrophenol in an aqueous medium. The Fourier transform infrared spectroscopy (FTIR) was used as a model instrument for the study of catalytic reduction of 4-nitrophenol using cationic-polystyrene-resin-bound silver nanocomposite materials. The mechanism is based on the reduction of 4-nitrophenol to 4-aminophenol due to the electron transfer process that occurred between donor borohydride (BH4−) and acceptor 4-nitrophenol. The polystyrene resin provides support and surface area to increase the catalytic activity of silver nanoparticles. The diffused reflectance-Fourier transform infrared spectroscopy revealed the binding of silver particles onto the surface of cationic polystyrene resin beads. Furthermore, the catalyst was easily separated by the filtration and drying process and was able to reuse. A quantitative analysis of this work has also been performed. The linearity range, the limit of detection, and the limit of quantification obtained for the present method were 0.1 × 10−4 to 1.0 M, 0.6 M, and 2.1 M, respectively. Moreover, a good catalytic efficiency was found to be 96.8%. The advantages of the current method are its simplicity, sensitivity, rapidity, low cost, ease of preparation, and excellent catalytic efficiency to reduce 4-nitrophenol from an aqueous solution.

Functionalized Silver and Gold Nanomaterials with Diagnostic and Therapeutic Applications

The functionalization of nanomaterials with suitable capping ligands or bioactive agents is an interesting strategy in designing nanosystems with suitable applicability and biocompatibility; the physicochemical and biological properties of these nanomaterials can be highly improved for biomedical applications. In this context, numerous explorations have been conducted in the functionalization of silver (Ag) and gold (Au) nanomaterials using suitable functional groups or agents to design nanosystems with unique physicochemical properties such as excellent biosensing capabilities, biocompatibility, targeting features, and multifunctionality for biomedical purposes. Future studies should be undertaken for designing novel functionalization tactics to improve the properties of Au- and Ag-based nanosystems and reduce their toxicity. The possible release of cytotoxic radicals or ions, the internalization of nanomaterials, the alteration of cellular signaling pathways, the translocation of these nanomaterials across the cell membranes into mitochondria, DNA damages, and the damage of cell membranes are the main causes of their toxicity, which ought to be comprehensively explored. In this study, recent advancements in diagnostic and therapeutic applications of functionalized Au and Ag nanomaterials are deliberated, focusing on important challenges and future directions.

Resin immobilized gold nanocomposites assisted surface enhanced infrared absorption (SEIRA) spectroscopy for improved surface assimilation of methylene blue from aqueous solution

In the present work, we report the adsorption of the methylene blue (MB) dye from an aqueous solution employing resin immobilized gold nanocomposites (R-AuNCs) assisted surface-enhanced infrared absorption (SEIRA) spectroscopy. The appropriate adsorption isotherm models, including the Langmuir, Freundlich, and Temkin are tested to reveal the interactive behavior between the adsorbent (R-AuNCs) and adsorbed (MB). Interestingly, Fourier transform infrared spectroscopy (FTIR) in combination with R-AuNC materials could be another approach through which the analysis of adsorption-desorption of MB on the surface of nanocomposite adsorbents is possible in a more precise way with high sensitivity and adsorptivity. In addition, a 10-fold enhancement of the signal intensity of MB dye was obtained due to the electrostatic interaction and H-bonding interaction between COO^- groups of adsorbent and the positively charged active sites of the dye molecules. The value of % removal efficiency and % adsorption obtained in the present method was 77.64% and 186.61%, respectively. Desorption of MB from adsorbent surface was also carried out using 0.1 M cetylpyridinium chloride as cationic surfactant; resulting process shows for 'n' number of cyclic process. The maximum desorption capacity for MB found in the present investigation was 44.38 mg/g, The advantages of current method are its simplicity, sensitivity, rapidity, ease to fabrication and excellent adsorption efficiencies to remove MB dye from aqueous solution.

LSPR-based colorimetric biosensing for food quality and safety

Ensuring consistently high quality and safety is paramount to food producers and consumers alike. Wet chemistry and microbiological methods provide accurate results, but those methods are not conducive to rapid, onsite testing needs. Hence, many efforts have focused on rapid testing for food quality and safety, including the development of various biosensors. Herein, we focus on a group of biosensors, which provide visually recognizable colorimetric signals within minutes and can be used onsite. Although there are different ways to achieve visual color-change signals, we restrict our focus on sensors that exploit the localized surface plasmon resonance (LSPR) phenomenon of metal nanoparticles, primarily gold and silver nanoparticles. The typical approach in the design of LSPR biosensors is to conjugate biorecognition ligands on the surface of metal nanoparticles and allow the ligands to specifically recognize and bind the target analyte. This ligand-target binding reaction leads to a change in color of the test sample and a concomitant shift in the ultraviolet-visual absorption peak. Various designs applying this and other signal generation schemes are reviewed with an emphasis on those applied for evaluating factors that compromise the quality and safety of food and agricultural products. The LSPR-based colorimetric biosensing platform is a promising technology for enhancing food quality and safety. Aided by the advances in nanotechnology, this sensing technique lends itself easily for further development on field-deployable platforms such as smartphones for onsite and end-user applications.

Au–Ag core–shell composite nanoparticles as a selective and sensitive plasmonic chemical probe for l-cysteine detection in Lens culinaris (lentils)

The present work reported is a simple and selective method for the colorimetrical detection of l-cysteine in Lens culinaris (or lentils) using Au–Ag core–shell (Au core Ag shell) composite nanoparticles as a chemical probe.