Rapid and inexpensive immunodiagnostic assays to monitor severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroconversion are essential for conducting large-scale COVID-19 epidemiological surveillance and profiling humoral responses against SARS-CoV-2 infections or immunizations. Herein, a colorimetic serological assay to detect SARS-CoV-2 IgGs in patients’ plasma was developed using short antigenic epitopes conjugated to gold nanoparticles (AuNPs). Four immunodominant linear B-cell epitopes, located on the spike (S) and nucleocapsid (N) proteins of SARS-CoV-2, were characterized for their IgG binding affinity and used as highly specific biological motifs on the nanoparticle to recognize target antibodies. Specific bivalent binding between SARS-CoV-2 antibodies and epitope-functionalized AuNPs trigger nanoparticle aggregation, which manifests as a distinct optical transition in the AuNPs’ plasmon characteristics within 30 min of antibody introduction. Co-immobilization of two epitopes improved the assay sensitivity relative to single-epitope AuNPs with a limit of detection of 3.2 nM, commensurate with IgG levels in convalescent COVID-19-infected patients. A passivation strategy was further pursued to preserve the sensing response in human plasma medium. When tested against 35 clinical plasma samples of varying illness severity, the optimized nanosensor assay can successfully identify SARS-CoV-2 infection with 100% specificity and 83% sensitivity. As the epitopes are conserved within the circulating COVID-19 variants, the proposed platform holds great potential to serve as a cost-effective and highly specific alternative to classical immunoassays employing recombinant viral proteins. These epitope-enabled nanosensors further expand the serodiagnostic toolbox for COVID-19 epidemiological study, humoral response monitoring, or vaccine efficiency assessment.

In aquaculture industry, fish, shellfish, and aquatic plants are cultivated in fresh, salt, or brackish waters. The increasing demand of aquatic products has stimulated the rapid growth of aquaculture industries. How to effectively monitor and control water quality is one of the key concerns for aquaculture industry to ensure high productivity and high quality. There are four major categories of water quality concerns that affect aquaculture cultivations, namely, (1) physical parameters, e.g., pH, temperature, dissolved oxygen, and salinity, (2) organic contaminants, (3) biochemical hazards, e.g., cyanotoxins, and (4) biological contaminants, i.e., pathogens. While the physical parameters are affected by climate changes, the latter three are considered as environmental factors. In this review, we provide a comprehensive summary of sensors, biosensors, and analytical technologies available for monitoring aquaculture water quality. They include low-cost commercial sensors and sensor network setups for physical parameters. They also include chromatography, mass spectrometry, biochemistry, and molecular methods (e.g., immunoassays and polymerase chain reaction assays), culture-based method, and biophysical technologies (e.g., biosensors and nanosensors) for environmental contamination factors. According to the different levels of sophistication of various analytical techniques and the information they can provide (either fine fingerprint, highly accurate quantification, semiquantification, qualitative detection, or fast screening), we will comment on how they may be used as complementary tools, as well as their potential and gaps toward current demand of real-time, online, and/or onsite detection.

In this paper, we report the utility of a colorimetric polymer stabilized cholesteric liquid crystal (PSCLC) array for detecting vaporous amines. The PSCLC with various polymer concentrations (5-20% w/w) is made into an array which shows distinct color changes upon exposure to 400 parts-permillion (ppm) octylamine vapor at 23-35 degrees C. Interestingly, PSCLC shows stronger response to primary amine over secondary amine, tertiary amine, ester, aldehyde, and alkane having similar molecular weights. PSCLCs also give detection limits as low as 2 ppmv for decylamine. Because PSCLC is transparent at room temperature and changes color upon exposure to amine vapors, it can be coated on windows or safety goggles to offer protection against amine vapors.