Robust colorimetric detection based on the anti-aggregation of gold nanoparticles for bromide in rice samples

Sensitive SERS assay for L-cysteine based on functionalized silver nanoparticles

L-cysteine, an indispensable amino acid present in natural proteins, plays pivotal roles in various biological processes. Consequently, precise and selective monitoring of its concentrations is imperative. Herein, we propose a Surface-enhanced Raman Scattering (SERS) sensor for detecting L-cysteine based on the anti-aggregation of 4-mercaptobenzoic acid (4-MBA) and histidine (His) functionalized silver nanoparticles (Ag NPs). The presence of Hg2+ ions can induce the aggregation of Ag NPs@His@4-MBA due to the unique nanostructures of Ag NPs@His@4-MBA, resulting in a robust SERS intensity of 4-MBA. However, in the presence of L-cysteine, the stronger affinity between L-cysteine and Hg2+ reduces the concentration of free Hg2+, causing the dispersion of the aggregated functionalized Ag NPs and the reduction of the SERS signal intensity of 4-MBA. The developed SERS platform demonstrates excellent performance with a low detection limit of 5 nM (S/N = 3) and linear detection capabilities within the range of 0.01-100 μM for L-cysteine. Additionally, the method was successfully employed for the determination of L-cysteine in spiked serum samples, yielding recoveries ranging from 95.0 % to 108.1 % with relative standard deviations of less than 3.3 %. This study not only presents a novel approach for fabricating highly sensitive and specific SERS biosensors for biomolecule detection but also offers a significant strategy for the development and construction of SERS substrates using anti-aggregation design.

Plasmonic nanoparticle's anti-aggregation application in sensor development for water and wastewater analysis

Colorimetric sensors have emerged as a powerful tool in the detection of water pollutants. Plasmonic nanoparticles use localized surface plasmon resonance (LSPR)-based colorimetric sensing. LSPR-based sensing can be accomplished through different strategies such as etching, growth, aggregation, and anti-aggregation. Based on these strategies, various sensors have been developed. This review focuses on the newly developed anti-aggregation-based strategy of plasmonic nanoparticles. Sensors based on this strategy have attracted increasing interest because of their exciting properties of high sensitivity, selectivity, and applicability. This review highlights LSPR-based anti-aggregation sensors, their classification, and role of plasmonic nanoparticles in these sensors for the detection of water pollutants. The anti-aggregation based sensing of major water pollutants such as heavy metal ions, anions, and small organic molecules has been summarized herein. This review also provides some personal insights into current challenges associated with anti-aggregation strategy of LSPR-based colorimetric sensors and proposes future research directions.

Advances in organic fluorescent probes for bromide ions, hypobromous acid and related eosinophil peroxidase-A review

Elemental bromine is among the essential elements for human health. In living organisms, bromide (Br^-) and hydrogen peroxide (H₂O₂) can be catalyzed by eosinophil peroxidase (EPO) to generate a reactive oxygen species (ROS), hypobromous acid (HOBr), which exhibits properties similar to those of hypochlorous acid (HOCl). Moreover, HOBr possesses strong oxidative and antibacterial properties, which are believed to play an important role in the neutrophil host defense system. However, overexpression or misexpression of HOBr can cause organismal and tissue damage, which is closely related to the development of various diseases. Therefore, an increasing number of studies has demonstrated physiological associations with the conversion of Br^- to HOBr. With the development of fluorescence imaging technology, developing fluorescent probes with novel structures and high selectivity to detect changes in Br^-, HOBr, and the related enzyme EPO levels in organisms has become very important. This paper summarizes Br^-, HOBr, and EPO fluorescent probes reported in recent years, including the design principles, mechanisms, optical properties, and bioapplications. Finally, the application prospects and challenges are also discussed.

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

Solid-phase colorimetric sensing probe for bromide based on a tough hydrogel embedded with silver nanoprisms

Sharp-tipped anisotropic silver (Ag) nanostructures are attracting increasing attention because of their unusual optical properties. However, the sharp tips make such nanostructures thermodynamically unstable; thus, they have been considered unsuitable for use in colorimetric sensing because of their tendency to aggregate or transform in a solution state. In the present study, a colorimetric sensing platform for detecting bromide (Br^-) in an aqueous medium was developed. The platform is based on the localized surface plasmon resonance (LSPR) properties of Ag nanoprisms with sharp tips. The key to using such Ag nanocrystals with extreme anisotropic structures is to adopt a solid-phase sensing platform. A Ag-nanoprism-embedded tough hydrogel with interpenetrating polymer networks was synthesized via aqueous-phase polymerization and crosslinking processes. The Ag nanoprisms immobilized inside the hydrogel were stable and did not exhibit aggregation or degradation over time; specifically, when the hydrogel was dried, the nanoprisms retained their inherent LSPR properties for an extended period. By taking advantage of the rapid and spontaneous morphological transformation of Ag nanoprisms inside the hybrid hydrogel exposed to Br^- and the corresponding changes in their LSPR properties, we designed a plasmonic sensing platform for the sensitive and selective detection of Br^- in an aqueous medium. The proposed colorimetric sensing platform was found to exhibit a wide sensing range and high selectivity, with a low limit of detection (LOD) of 10 μM, and offers substantial advantages over previously developed systems; specifically, it is portable, eco-friendly, safe to use and handle, stable for extended periods, and enables naked-eye detection. We believe that the as-proposed sensing platform can be used as a point-of-care analytical tool for detecting Br^- in a broad range of samples.

Ionic Strength Influences on Biofunctional Au-Decorated Microparticles for Enhanced Performance in Multiplexed Colorimetric Sensors

The rising development of biosensors offers a great potential for health, food, and environmental monitoring. However, in many colorimetric platforms, there is a performance limitation stemming from the tendency of traditional Au nanoparticles toward nonspecific aggregation in response to changing ionic strength (salt concentration). This work puts forward a new type of colorimetric aptamer-functionalized labeling of microparticles, which allows to leverage an increase in ionic strength as a positive driver of enhanced detection performance of analytical targets. The resulting device is a cost-effective, instrument-free, portable, and reliable aptasensor that serves as basis for the fabrication of universal paper-based colorimetric platforms with the capability of multiplex, multireplicates and provides quantitative colorimetric detection. A controlled fabrication process was demonstrated by keeping 90% of the signal obtained from the as-fabricated devices (n = 40) within ± 1 standard deviation (SD) (relative SD = 5.69%) and following a mesokurtic normal-like distribution (p = 0.385). We propose for the first time a salt-induced aggregation mechanism for highly stable multilayered label particles (ssDNA-PEI-Au-PS) as the basis of the detection scheme. The use of DNA aptamers as capture biomolecules and PEI as an encapsulating agent allows for a sensitive and highly specific colorimetric response. As a proof of concept, multiplexed detection of mercury (Hg²⁺) and arsenic (As³⁺) was demonstrated. In addition, we introduced a robust image analysis algorithm for testing zone segmentation and color signal quantification that allowed for analytical detection, reaching a limit of detection of 1 ppm for both targeted analytes, with enough evidence (p > 0.05) to prove the high specificity of the fabricated device versus a pool of possible interferent ions.

Optical Detection of Bromide Ions Using Pt(II)-5,10,15,20-Tetra-(4-methoxy-phenyl)-porphyrin

Bromide ions are present in many environments, such as sedative drugs, methyl-bromide-treated vegetables and seawater. Excess bromide in humans interferes with iodide metabolism and is considered toxic. The need for fast and inexpensive methods for bromide detection is of interest. Spectrophotometric detection methods provide accurate and sensitive results. The well-known ability of metalloporphyrins to bind anionic ligands to the central metal ion has been exploited. The changes in the optical properties of Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) under the influence of bromide ions allowed us to achieve a fast, simple and reliable UV-vis spectrophotometric method of detection with a detection limit of 2.5 × 10−8 M and a good confidence coefficient: 99.05%. The potential interfering ions, such as Cl−, I−, NO2−, NO3−, SCN−, SO32−, SO42− and PO43− of 100-fold higher and Cl− and R-S− of 1000-fold higher concentrations in the mixture as compared to the determined concentration of bromide ions (c = 10−5 M), were tested and did not influence the results. The behavior of the sensitive porphyrin in various pH media was investigated in order to determine their influence upon the bromide detection capacity.