Behavioral changes and neurochemical responses in Chinese rare minnow exposed to four psychoactive substances.

With the increase use of psychoactive pharmaceuticals, these substances and their metabolites are frequently detected in aquatic environment. However, there is still a knowledge gap in the neurotoxicity of these pollutants on aquatic organisms as well as related behavioral effects. In this study, the effects of four psychoactive substances alprazolam (ALPZ), lorazepam (LORZ), codeine (COD) and morphine (MOR) were investigated on 23 neurochemicals and 5 behaviors in Chinese rare minnow (Gobiocypris rarus). The comprehensive neurotoxicity was then evaluated at three levels of neurochemical, neurotransmitter system and comprehensive index. The results indicated that ALPZ and LORZ not only increased serotonin and dopamine along with the decrease of glutamic acid, but also depressed the locomotory activity of Chinese rare minnow although without significance. Exposure to COD and MOR increased acetylcholine, dopamine and adrenaline, and significantly increased anxiety-related behaviors of Chinese rare minnow. Comprehensive evaluation showed that COD has the lowest neurotoxic effect on Chinese rare minnow. LORZ shows a stronger neurotoxicity at low concentration of exposure than the other three substances. MOR has the highest neurotoxic effect at high concentration of exposure among the four drugs. The findings revealed the comprehensive neurotoxicity of these psychoactive substances in fish and suggested ecological risks of these pollutants in aquatic environment.

A filtration-assisted approach to enhance optical detection of analytes and its application in food matrices.

Analysis of target analytes in food and environmental samples often required sophisticated instrumentation, which restrains the accessibility and portability of the analysis. Herein, we developed an instrument-free approach for rapid quantification of target analytes. The reported filtration-assisted approach enables image analysis of aggregates formed via interaction between analytes and silver nanoparticles (AgNPs). Two model analytes were chosen for aggregating AgNPs, potassium phosphate for neutralizing the charges and a di-thiol molecule (2,2'-(ethylenedioxy) diethanethiol (EDT)) for cross-linking. The mixtures of AgNPs and analytes were filtered onto filter membranes and analyzed using grey color intensity analysis. Based on the AgNPs-EDT platform, we demonstrated the detection of 1 µg/mL acrylamide in instant coffee and biscuit matrices was achievable. The filtration-assisted method provides a simple, fast and inexpensive approach for optical detection and quantification of analytes in food matrices.

Occurrence and risk assessment of psychoactive substances in tap water from China.

Psychoactive substances are becoming a new concern in aquatic environment along with the increase in use of these substances. In this study, 23 psychoactive substances were investigated in the tap water collected in 63 sites in China. Eighteen out of 23 psychoactive substances were detected at the range of < method detection limits (MDLs) to 24.9 ng L-1. It was found that diazepam and temazepam were the major psychoactive substances in the tap water with the median concentration of 1.0 and 0.06 ng L-1, respectively. The high exposure dose for each psychoactive substance was calculated from 0.6 to 855 pg kg-1 bw d-1 and showed an order of men ≥ boys ≥ girls ≥ women. Risk assessment revealed there was little risk of psychoactive substances on human health at current residual levels.

Comparison of label-free and label-based approaches for surface-enhanced Raman microscopic imaging of bacteria cells.

Surface-enhanced Raman spectroscopic (SERS) approaches are emerging for bacteria analysis whereby bacteria cells can be measured based on their biochemical composition (label-free) or with the aid of a chemical label to enhance the SERS signal. Combining a microscope, SERS microscopy is capable of imaging bacteria populations en masse based on specific spectrophotometric peaks. Here, we compared the label-free and label-based approaches to study Escherichia coli O157:H7 that was utilized as a model bacterium for SERS imaging analyses. Gold (Au) nanoparticles were utilized to enhance Raman scattering during this study and 3-mercaptophenylboronic acid was utilized as a model chemical label for comparison against label-free conditions. The result shows that SERS images of bacteria cells yielded measurable differences in precision, depending on the application of chemical labels. Chemical labels enabled SERS imaging of whole bacteria populations with single-cell precision. Bacteria coated with labels were also easier to bring into focus using high-magnification optical microscopy, without the need for immersion oil. Label-free analyses of single-cells were lower in geographic precision but provided opportunities to study the natural biochemistry of bacteria cells with strong accuracy. SERS analyses of label-free bacteria cell components were conclusively improved in vitro on a time-dependent basis. This concept can serve as an important benchmark when biochemically profiling or characterizing bacteria cells based on SERS. Electron micrographs proved that chemical labels can be utilized to increase nanoparticle contact with bacteria cells and reduce free nanoparticles that contribute to background noise in SERS spectra. We also demonstrate the use of both 3-mercaptophenylboronic acid and propidium iodide to discriminate live and dead bacteria through the simultaneous collection of data from these two chemical labels. Label-free approaches to SERS bacteria analyses are better suited for biochemical characterization and label-based approaches are better suited when accounting for individual cells among a population.

Development of a filtration-based SERS mapping platform for specific screening of Salmonella enterica serovar Enteritidis.

The presence of Salmonella in natural freshwater and drinking water is a leading cause of intestinal illness all over the world; thus, the detection of Salmonella in water is of great importance to public health. The objective of this study is to develop a rapid screening method for the detection of Salmonella enterica serovar Enteritidis in water involving surface-enhanced Raman spectroscopy (SERS), aptamers, and filtration. SERS offers a great alternative to traditional methods of pathogen detection, with a simplified detection assay and shortened detection time. The specific capturing and labeling of Salmonella Enteritidis are realized by a specific single-stranded DNA aptamer, which is modified with an additional chain of adenine and fluorescein (FAM) and used as presence/absence indicator of Salmonella Enteritidis. By incorporating a vacuum filtration system, bacterial cells recognized by the specific aptamer are concentrated onto a membrane. With additional filtration of gold nanoparticles, the aptamer signals were captured and used to construct a SERS mapping indicating the presence and absence of target bacterial strains with potential quantitative capability. The specificity of the method was validated by using other strains of bacteria such as Escherichia coli and Listeria monocytogenes. The sensitivity of the method goes down to 103 CFU/mL for 1 mL of sample with a total detection and analyzing time within 3 h. This study demonstrates the capability of the filtration-based SERS platform for detecting Salmonella Enteritidis in various aqueous matrices such as distilled water and rinsing water from fresh produce with high selectivity and sensitivity. Graphical abstract.

In situ colorimetric detection of glyphosate on plant tissues using cysteamine-modified gold nanoparticles.

Monitoring the levels of pesticides on plant tissues is important for achieving effective protection of crops after application, as well as ensuring low levels of residues during harvest. In this study, a simple, rapid, and fieldable colorimetric method for detecting the pesticide glyphosate (Gly) on the plant tissues in situ using cysteamine-modified gold nanoparticles (AuNPs-Cys) has been developed. The aggregation of AuNPs-Cys in the presence of Gly results in a consequent color change from red to blue (or purple), which could be observed visually on the surface of plant tissues. With the naked eye, we successfully detected Gly spiked on the surface of spinach, apple, and corn leaves in situ. Further verification and quantification were achieved using surface-enhanced Raman spectroscopy (SERS) which uses AuNPs-Cys as the substrate. Moreover, application of this method was demonstrated through the evaluation of the Gly distribution on plant tissues which could greatly facilitate the development of precision agriculture technology.

Mapping bacteria on filter membranes, an innovative SERS approach.

The existence of pathogenic bacteria in drinking water has been a threat to the safety of human well-being. Traditional methods to detect bacteria are standard plate counts or rapid methods such as ELISA and PCR. However, those methods can be time-consuming or require pre-enrichment when detecting low concentrations of bacteria. Filter membrane has been used for bacteria collection and culturing when monitoring environmental water samples. In this study, we applied surface enhanced Raman spectroscopy (SERS) to rapidly screen bacteria cells on a filter membrane based on the unique signal from an indicator molecule, 4-mercaptophenylboronic acid (4-mpba), that can specifically bind to the surface of bacteria through diol group in its structure and give off consistent SERS signal. With a pore size of 0.22 µm, the filter membrane functions as both a concentrating device and a separation mechanism that eliminates molecules smaller than the pore size. With SERS mapping, 4-mpba gives characteristic signal, indicating the presence of bacteria, whereas no 4-mpba signal was observed in the absence of bacteria. The developed method can detect Escherichia coli, Salmonella enterica, and Listeria monocytogenes on a filter membrane non-selectively in 80 min. Application of the method in pond water was demonstrated. However, this method may not be able to discriminate between live and dead bacterial cells and further development is needed.

Rationalizing and advancing the 3-MPBA SERS sandwich assay for rapid detection of bacteria in environmental and food matrices.

Bacterial foodborne illness continues to be a pressing issue in our food supply. Rapid detection methods are needed for perishable foods due to their short shelf lives and significant contribution to foodborne illness. Previously, a sensitive and reliable surface-enhanced Raman spectroscopy (SERS) sandwich assay based on 3-mercaptophenylboronic acid (3-MBPA) as a capturer and indicator molecule was developed for rapid bacteria detection. In this study, we explored the advantages and constraints of this assay over the conventional aerobic plate count (APC) method and further developed methods for detection in real environmental and food matrices. The SERS sandwich assay was able to detect environmental bacteria in pond water and on spinach leaves at higher levels than the APC method. In addition, the SERS assay appeared to have higher sensitivity to quantify bacteria in the stationary phase. On the other hand, the APC method was more sensitive to cell viability. Finally, a method to detect bacteria in a challenging high-sugar juice matrix was developed to enhance bacteria capture. This study advanced the SERS technique for real applications in environment and food matrices.

A Filter-based Surface Enhanced Raman Spectroscopic Assay for Rapid Detection of Chemical Contaminants.

We demonstrate a method to fabricate highly sensitive surface-enhanced Raman spectroscopic (SERS) substrates using a filter syringe system that can be applied to the detection of various chemical contaminants. Silver nanoparticles (Ag NPs) are synthesized via reduction of silver nitrate by sodium citrate. Then the NPs are aggregated by sodium chloride to form nanoclusters that could be trapped in the pores of the filter membrane. A syringe is connected to the filter holder, with a filter membrane inside. By loading the nanoclusters into the syringe and passing through the membrane, the liquid goes through the membrane but not the nanoclusters, forming a SERS-active membrane. When testing the analyte, the liquid sample is loaded into the syringe and flowed through the Ag NPs coated membrane. The analyte binds and concentrates on the Ag NPs coated membrane. Then the membrane is detached from the filter holder, air dried and measured by a Raman instrument. Here we present the study of the volume effect of Ag NPs and sample on the detection sensitivity as well as the detection of 10 ppb ferbam and 1 ppm ampicillin using the developed assay.