Colorimetric assay based on arginine-functionalized gold nanoparticles for the detection of dibutyl phthalate in Baijiu samples

Indicator displacement-based colorimetric assay for dibutyl phthalate in pharmaceutical products with titanium(IV)-pyridylazo resorcinol (PAR)

Taking advantage of the competitive binding affinity towards Ti(IV) between 4-(2-pyridylazo) resorcinol (PAR) and phthalate, a simple indicator displacement (ID)-based colorimetric assay was designed for indirect determination of a well-known phthalic acid ester, dibutyl phthalate (DBP). The indicator PAR and Ti(IV) formed a purplish-red-colored Ti(IV)-PAR complex (λmax = 540 nm) at a 1:1 ratio. In the presence of pre-hydrolyzed DBP, colorless complex formation of phthalate ion (emerging from alkaline hydrolysis of DBP) with Ti(IV) resulted in a hypsochromic shift in absorbance maximum, accompanying a color change from purplish-red to yellowish-orange (λmax = 390 nm) by the release of PAR from Ti(IV)-PAR system. Based on this mechanism, the linear response range of the system for DBP was found to lie between 0.16 and 0.37 mmol L-1 with an experimental detection limit of 11.6 µmol L-1. The recommended Ti(IV)-PAR system was successfully applied to DBP-containing pharmaceutical products (as real sample) after a simple clean-up process for removing possible water-soluble interferents. The analytical results obtained from the recommended method (by applying the standard addition approach) and the reference liquid chromatography-tandem mass spectrometric (LC-MS/MS) method were statistically compared using DBP-extract of the drug samples. Consequently, a simple and selective colorimetric ID strategy was proposed for the analysis of DBP in pharmaceuticals for the first time.

Accurately recognizing chromium species with multi-functionalized nano Au-based sensor array

High-resolution identification of chromium (Cr) species, especially various organic-Cr complexes, in a convenient and economically-feasible manner is the prerequisite for achieving the advanced treatment of chromium wastewater. To this end, a colorimetric nano-Au sensor array was developed by taking advantage of the UV-spectra shift of gold nanoparticles (Au NPs) upon interaction with Cr species; specifically, four molecular modifiers [i.e., iminodiacetic acid (IDA), tripolyphosphate (TPP), cetyltrimethylammonium bromide (CTAB), and 1,5-diphenylcarbazide (DPC)] were intentionally employed for assembling nano-Au array receptors, which showed respective responses toward different Cr species through the formation of coordination, hydrophobic interaction, electrostatic attraction, and redox reaction, respectively; the "fingerprint" differences of the unique optical properties were then integrated for semi-quantitatively recognizing Cr species by pattern recognition techniques. Eleven ubiquitous Cr species [i.e., Cr(III), Cr(VI), and various Cr(III)-organic complexes] served as the model samples, which could be sensitively identified, no matter in individual or mixture mode, by the developed nano-Au sensor array on the basis of the colorimetric responses resulted from diverse nano-Au-aggregation behaviors, with excellent anti-interference ability in the simulated or actual water scenario. Attractively, the nano-Au sensor array can achieve very sensitive detection limit of the quantitative analyses of Cr species in a prompt in-situ manner, which usually requires a two-step process of separation and detection for the conventional analytical methods. Such a convenient strategy of Cr species discrimination conduces to rationally designing specific protocols for the advanced treatment of chromium wastewater.

Nanotechnology-based optical sensors for Baijiu quality and safety control

Baijiu quality and safety have received considerable attention owing to the gradual increase in its consumption. However, owing to the unique and complex process of Baijiu production, issues leading to quality and safety concerns may occur during the manufacturing process. Therefore, establishing appropriate analytical methods is necessary for Baijiu quality assurance and process control. Nanomaterial (NM)-based optical sensing techniques have garnered widespread interest because of their unique advantages. However, comprehensive studies on nano-optical sensing technology for quality and safety control of Baijiu are lacking. In this review, we systematically summarize NM-based optical sensor applications for the accurate detection and quantification of analytes closely related to Baijiu quality and safety. Furthermore, we evaluate the sensing mechanisms for each application. Finally, we discuss the challenges nanotechnology poses for Baijiu analysis and future trends. Overall, nanotechnological approaches provide a potentially useful alternative for simplifying Baijiu analysis and improving final product quality and safety.

Rapid visual dual-mode detection of Zr(IV) based on L-histidine functionalized gold nanoparticles

Heavy metal pollution has always been a great threat to human health and safety. Compared with other heavy metals, although zirconium ion (Zr(IV)) is equally harmful, due to the lack of research on Zr(IV) in the biological systems and environment, its detection does not seem to have received the attention it deserves. Herein, a rapid visual dual-mode detection (colorimetric and chrominance method) of Zr(IV) based on L-histidine functionalized gold nanoparticles (HIS-AuNPs) has been reported. AuNPs and HIS-AuNPs before and after adding Zr(IV) were characterized by UV-Vis, TEM, DLS, Zeta potential, EDS and FT-IR, etc. These results showed that L-histidine was successfully modified on the surface of AuNPs by forming a stable Au-N bond, and its modification had little effect on the dispersion degree of AuNPs. After the addition of Zr(IV), interaction of this metal ion with the imidazolyl group on L-histidine can obviously cause the aggregation of HIS-AuNPs within 12 min, and the dispersion state and particle size of HIS-AuNPs can be significantly changed. These two detection modes were established by means of absorbance and color change of solution, and being used in addition and recovery experiments of Zr(IV) in natural water. Under the optimal conditions, these two modes exhibited good linearity within 15-70 and 20-100 μmol L-1, and limit of detection of 2.62 and 6.25 μmol L-1. The proposed method was highly sensitive and selective, which provided a new convenient way to realize the detection of Zr(IV).

Fibrillation of Human Serum Albumin Differentially Affected by Asp-, Arg-, and Tyr-Capped Gold Nanoparticles

Fibrillation of proteins is associated with a number of debilitating diseases, including various neurodegenerative disorders. Prevention of the protein fibrillation process is therefore of immense importance. We investigated the effect of amino acid-capped AuNPs on the prevention of the fibrillation process of human serum albumin (HSA), a model protein. Amino acid-capped AuNPs of varying sizes and agglomeration extents were synthesized under physiological conditions. The AuNPs were characterized by their characteristic surface plasmon resonance (SPR), and their interactions with HSA were investigated through emission spectroscopy in addition to circular dichroism (CD) spectral analyses. Fluorescence lifetime imaging (FLIM) as well as transmission electron microscopy (TEM) were used to observe the fibrillar network. Thermodynamic and kinetic analyses from CD and fluorescence emission spectra provided insights into the fibrillation pathway adopted by HSA in the presence of capped AuNPs. Kinetics of the fibrillation pathway followed by ThT fluorescence emission confirmed the sigmoidal nature of the process. The highest cooperativity was observed in the case of Asp-AuNPs with HSA. This was in accordance with the ΔG value obtained from the CD spectral analyses, where Arg-AuNPs with HSA showed the highest positive ΔG value and Asp-AuNPs with HSA showed the most negative ΔG value. The study provides information about the potential use of conjugate AuNPs to monitor the fibrillation process in proteins.

Ultrasensitive, Label-Free Voltammetric Detection of Dibutyl Phthalate Based on Poly-l-lysine/poly(3,4-ethylenedioxythiophene)-porous Graphene Nanocomposite and Molecularly Imprinted Polymers

Development of an efficient technique for accurate and sensitive dibutyl phthalate (DBP) determination is crucial for food safety and environment protection. An ultrasensitive molecularly imprinted polymers (MIP) voltammetric sensor was herein engineered for the specific determination of DBP using poly-l-lysine/poly(3,4-ethylenedioxythiophene)/porous graphene nanocomposite (PLL/PEDOT-PG) and poly(o-phenylenediamine)-imprinted film as a label-free and sensing platform. Fabrication of PEDOT-PG nanocomposites was achieved through a simple liquid-liquid interfacial polymerization. Subsequently, poly-l-lysine (PLL) functionalization was employed to enhance the dispersibility and stability of the prepared PEDOT-PG, as well as promote its adhesion on the sensor surface. In the presence of DBP, the imprinted poly(o-phenylenediamine) film was formed on the surface of PLL/PEDOT-PG. Investigation of the physical properties and electrochemical behavior of the MIP/PLL/PEDOT-PG indicates that the incorporation of PG into PEDOT, with PLL uniformly wrapping its surface, significantly enhanced conductivity, carrier mobility, stability, and provided a larger surface area for specific recognition sites. Under optimal experimental conditions, the electrochemical response exhibited a linear relationship with a logarithm of DBP concentration within the range of 1 fM to 5 µM, with the detection limit as low as 0.88 fM. The method demonstrated exceptional stability and repeatability and has been successfully applied to quantify DBP in plastic packaging materials.

Exploring Various Photochemical Processes in Optical Sensing of Pesticides by Luminescent Nanomaterials: A Concise Discussion on Challenges and Recent Advancements

Food safety is a burning global issue in this present era. The prevalence of harmful food additives and contaminants in everyday food is a significant cause for concern as they can adversely affect human health. More particularly, among the different food contaminants, the use of excessive pesticides in agricultural products is severely hazardous. So, the optical detection of residual pesticides is an effective strategy to counter the hazardous effect and ensure food safety. In this perspective, nanomaterials have played a leading role in defending the open threat against food safety instigated by the reckless use of pesticides. Now, nanomaterial-based optical detection of pesticides has reached full pace and needs an inclusive discussion. This Review covers the advancement of photoprocess-based optical detection of pesticides categorically using nanomaterials. Here, we have thoroughly dissected the photoprocesses (aggregation and aggregation-induced emission (AIE), charge transfer and intramolecular charge transfer (ICT), electron transfer and photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), hydrogen bonding, and inner filter effect) and categorically demarcated their significant role in the optical detection of pesticides by luminescent nanomaterials over the last few years.

A review on solution- and vapor-responsive sensors for the detection of phthalates

Phthalic acid esters, largely referred to as phthalates, are today acknowledged as important pollutants used in the manufacture of polyvinyl chloride (PVC)-based plastics, whose use extends to almost every aspect of modern life. The risk of exposure to phthalates is particularly relevant as high concentrations are regularly found in drinking water, food-contact materials and medical devices, motivating an immense body of research devoted to methods for their detection in liquid samples. Conversely, phthalate vapors have only recently been acknowledged as potentially important atmospheric pollutants and as early fire indicators; additionally, deposition of these vapors can pose significant problems to the proper functioning of spacecraft and diverse on-board devices, leading to major space agencies recognizing the need of developing vapor-responsive phthalate sensors. In this manuscript we present a literature survey on solution- and vapor-responsive sensors and analytical assays for the detection of phthalates, providing a detailed analysis of a vast array of analytical data to offer a clear idea on the analytical performance (limits of detection and quantification, linear range) and advantages provided by each class of sensor covered in this review (electrochemical, optical and vapor-responsive) in the context of their potential real-life applications; the manuscript also gives detailed fundamental information on the various physicochemical responses exploited by these sensors and assays that could potentially be harnessed by new researchers entering the field.

Construction of multiple modes using gold nanoparticles as probes for the rapid detection of fenpyroximate

Herein, three patterns for the detection of fenpyroximate based on the response signal of gold nanoparticles are described. The strong interaction between the guanidine group of arginine-modified gold nanoparticles and the ester group of fenpyroximate led to the aggregation of the nanoparticles and to a variation of ultraviolet-visible light spectrum and color of the solution. Sensors were constructed based on the correlation of the concentration of fenpyroximate with the absorbance ratio (A₆₅₀/A₅₂₅) and the R value was obtained by extracting the color of the test solution by using a smartphone to take a photo of the solution, which was then analyzed by colorimeter software. The absorbance ratio increased linearly in the range of 0.225-0.375 mg L^-1 and the limit of detection was 0.215 mg L^-1, while the R value declined linearly in the range of 0.20-0.40 mg L^-1 and the limit of detection was 0.21 mg L^-1. Further, the gold nanoparticles could cause a fluorescence quenching of fluorescent dyes, such as rhodamine B, and it was found that the fluorescence could be quenched and then restored after aggregation; therefore, a fluorescence method based on fluorescence "off-on" was constructed, and the fluorescence quenching was found to increase linearly in the range of 0.0-1.0 mg L^-1 and the limit of detection was 0.013 mg L^-1. These three patterns indicated highly selective and sensitive response signals for fenpyroximate, and all were applied to the detection of fenpyroximate in apple juice, pear juice, and environmental water samples, with the results showing that the three methods could be mutually verified, with the recoveries ranging from 94.15% to 110.65%.