Visual and Colorimetric Sensing of Metsulfuron-Methyl by Exploiting Hydrogen Bond-Induced Anti-Aggregation of Gold Nanoparticles in the Presence of Melamine

Gold nanoparticle-based optical nanosensors for food and health safety monitoring: recent advances and future perspectives

Modern society has been facing serious health-related problems including food safety, diseases and illness. Hence, it is urgent to develop analysis methods for the detection and control of food contaminants, disease biomarkers and pathogens. As the traditional instrumental methods have several disadvantages, including being time consuming, and having high cost and laborious procedures, optical nanosensors have emerged as promising alternative or complementary approaches to those traditional ones. With the advantages of simple preparation, high surface-to-volume ratio, excellent biocompatibility, and especially, unique optical properties, gold nanoparticles (AuNPs) have been demonstrated as excellent transducers for optical sensing systems. Herein, we provide an overview of the synthesis of AuNPs and their excellent optical properties that are ideal for the development of optical nanosensors based on local surface plasmon resonance (LSPR), colorimetry, fluorescence resonance energy transfer (FRET), and surface-enhanced Raman scattering (SERS) phenomena. We also review the sensing strategies and their mechanisms, as well as summarizing the recent advances in the monitoring of food contaminants, disease biomarkers and pathogens using developed AuNP-based optical nanosensors in the past seven years (2015-now). Furthermore, trends and challenges in the application of these nanosensors in the determination of those analytes are discussed to suggest possible directions for future developments.

A novel colorimetric biosensor for sensitive detection of aflatoxin mediated by bacterial enzymatic reaction in saffron samples

Aflatoxin is regarded as the potent carcinogenic agent which is secreted from fungi and present in some food products. So far, many detection methods have been developed to determine the trace amounts of aflatoxin in foods. In the present study a colorimetric competitive assay for detection of aflatoxin B1 (AFB1) has been developed based on interaction of gelatin functionalized gold nanoparticles (AuNPs@gelatin) in specific enzymatic reaction. Bacterial supernatant containing gelatinase enzyme were used as the substrate that could digest the coated gelatin on the surface of AuNPs and following in the presence of NaCl medium ingredient resulted to color change of AuNPs colloidal solution from red to purple. It was observed that with addition of aflatoxin to the bacterial supernatant, aflatoxin could interfere in aggregation of AuNPs and inhibited the process which subsequently prevent the expected color change induced by AuNPs aggregation. The supernatant containing AuNPs were investigated to analyze their induced surface plasmon resonance spectra through UV-visible spectroscopy. The absorption values were directly proportional with the applied AFB1 concentration. The experiment conditions including incubation time, AuNPs concentration and pH were investigated. The obtained results showed that through this approach we could detect the AFB1 in a linear range from 10 to 140 pg ml^-1, with detection limit of 4 pg ml^-1. Real sample assay in saffron samples showed recoveries percentage of 92.4%-95.3%. The applied approach proposed simple, cost effective and specific method for detection of AFB1 toxin in food samples.

Recent Advances and Perspectives of Molecularly Imprinted Polymer-Based Fluorescent Sensors in Food and Environment Analysis

Molecular imprinting technology (MIT), also known as molecular template technology, is a new technology involving material chemistry, polymer chemistry, biochemistry, and other multi-disciplinary approaches. This technology is used to realize the unique recognition ability of three-dimensional crosslinked polymers, called the molecularly imprinted polymers (MIPs). MIPs demonstrate a wide range of applicability, good plasticity, stability, and high selectivity, and their internal recognition sites can be selectively combined with template molecules to achieve selective recognition. A molecularly imprinted fluorescence sensor (MIFs) incorporates fluorescent materials (fluorescein or fluorescent nanoparticles) into a molecularly imprinted polymer synthesis system and transforms the binding sites between target molecules and molecularly imprinted materials into readable fluorescence signals. This sensor demonstrates the advantages of high sensitivity and selectivity of fluorescence detection. Molecularly imprinted materials demonstrate considerable research significance and broad application prospects. They are a research hotspot in the field of food and environment safety sensing analysis. In this study, the progress in the construction and application of MIFs was reviewed with emphasis on the preparation principle, detection methods, and molecular recognition mechanism. The applications of MIFs in food and environment safety detection in recent years were summarized, and the research trends and development prospects of MIFs were discussed.

Dual sensing reporter system of assembled gold nanoparticles toward the sequential colorimetric detection of adenosine and Cr(III)

A facile and sensitive sequential colorimetric detection strategy for adenosine and Cr³⁺ has been presented by using the aptamer and 11-mercaptoundecanoic acid assembled gold nanoparticles. The thiolated DNA and 11-mercaptoundecanoic acid was simultaneously assembled to the surface of gold nanoparticles in one step by gold-sulfur interaction. Adenosine aptamer was linked to functionalized gold nanaoparticles based on the strict complementary nature of the DNA base pairs. Conformational change of aptamer will be induced due to its specific binding with targets. As a result, this aptamer tethered aggregated nanoparticles underwent fast disassembly into dispersed nanoparticles upon binding of adenosine, and this distance change between particles induced a distinct solution color changing from blue to red. The dispersed particles were sensitive to Cr³⁺ due to the chelation effect between the carboxyl group of 11-mercaptoundecanoic acid and metal ions, and further occurred obvious aggregation accompanying with a color change from red to blue. Depended on this principle, a sensitive and selective sequential colorimetric sensor for detection of adenosine and Cr³⁺ was developed. The proposed colorimetric sensor exhibited wide linear ranges and low detection limits towards the detection of adenosine and Cr³⁺. Regarding adenosine, linear range was 1 × 10^-7 ∼ 1 × 10^-4 M with low detection limit of 1.8 × 10^-8 M, and the naked eye detection limit was estimated as 20 μM. With regard to Cr³⁺, good linear relationship was ranged from 1 × 10^-10 to 1 × 10^-6 M with low detection limit of 1.7 × 10^-11 M，and the naked eye detection limit was as low as 0.1 nM. Meanwhile, bifunctional recognition was successfully used for practical human urine samples with good recoveries from 89.0% to 112.6% for adenosine and 90.2%-113.4% for Cr³⁺. It also highlights the potential applications of other aptamers and ligands in cascade analysis of other analytes.

A review on nanomaterial-based electrochemical, optical, photoacoustic and magnetoelastic methods for determination of uranyl cation

This review (with 177 refs) gives an overview on nanomaterial-based methods for the determination of uranyl ion (UO₂²⁺) by different types of transducers. Following an introduction into the field, a first large section covers the fundamentals of selective recognition of uranyl ion by receptors such as antibodies, aptamers, DNAzymes, peptides, microorganisms, organic ionophores (such as salophens, catechols, phenanthrolines, annulenes, benzo-substituted macrocyclic diamides, organophosphorus receptors, calixarenes, crown ethers, cryptands and β-diketones), by ion imprinted polymers, and by functionalized nanomaterials. A second large section covers the various kinds of nanomaterials (NMs) used, specifically on NMs for electrochemical signal amplification, on NMs acting as signal tags or carriers for signal tags, on fluorescent NMs, on NMs for colorimetric assays, on light scattering NMs, on NMs for surface enhanced Raman scattering (SERS)-based assays and wireless magnetoelastic detection systems. We then discuss detection strategies, with subsections on electrochemical methods (including ion-selective and potentiometric systems, voltammetric systems and impedimetric systems). Further sections treat colorimetric, fluorometric, resonance light scattering-based, SERS-based and photoacoustic methods, and wireless magnetoelastic detection. The current state of the art is summarized, and current challenges are discussed at the end. Graphical abstract An overview is given on nanomaterial-based methods for the detection of uranyl ion by different types of transducers (such as electrochemical, optical, photoacoustic, magnetoelastic, etc) along with a critical discussion of their limitations, benefits and application to real samples.

Application of Gold-Nanoparticle Colorimetric Sensing to Rapid Food Safety Screening

Due to their unique optical properties, narrow size distributions, and good biological affinity, gold nanoparticles have been widely applied in sensing analysis, catalytic, environmental monitoring, and disease therapy. The color of a gold nanoparticle solution and its maximum characteristic absorption wavelength will change with the particle size and inter-particle spacing. These properties are often used in the detection of hazardous chemicals, such as pesticide residues, heavy metals, banned additives, and biotoxins, in food. Because the gold nanoparticles-colorimetric sensing strategy is simple, quick, and sensitive, this method has extensive applications in real-time on-site monitoring and rapid testing of food quality and safety. Herein, we review the preparation methods, functional modification, photochemical properties, and applications of gold nanoparticle sensors in rapid testing. In addition, we elaborate on the colorimetric sensing mechanisms. Finally, we discuss the advantages and disadvantages of colorimetric sensors based on gold nanoparticles, and directions for future development.

Anti-Agglomeration Behavior and Sensing Assay of Chlorsulfuron Based on Acetamiprid-Gold Nanoparticles

Monitoring of low levels of chlorsulfuron in environmental water samples is important. Although several detection methods have been developed, they all have some drawbacks, such as being time-consuming, requiring expensive instruments and experienced operators, and consuming large volumes of organic solvents. There is an urgent need for a simple, rapid, and inexpensive detection method for chlorsulfuron. Herein, such a method was developed using anti-aggregation of gold nanoparticles (AuNPs) in the presence of acetamiprid in agricultural irrigation water samples. Aggregation of the AuNPs was induced by acetamiprid, and this produced a distinct color change from Bordeaux red to blue. However, the strong hydrogen bonding interaction between chlorsulfuron and acetamiprid could inhibit AuNP aggregation. The effect of chlorsulfuron on the anti-agglomeration behavior of AuNPs was monitored by ultraviolet–visiblespectroscopy (UV-Vis) and the naked eye over a concentration range 0.1–100 mg/L. The detection limit for chlorsulfuron was 0.025 mg/L (signal-to-noise ratio of three). This colorimetric method was successfully applied to the determination of chlorsulfuron in spiked tap water and agricultural irrigation water with satisfactory recoveries (76.3%–94.2%).