Paper-based microfluidic chip for rapid detection of SARS-CoV-2 N protein

This research has developed a method for rapid detection of SARS-CoV-2 N protein on a paper-based microfluidic chip. The chitosan-glutaraldehyde cross-linking method is used to fix the coated antibody, and the sandwich enzyme-linked immunosorbent method is used to achieve the specific detection of the target antigen. The system studied the influence of coating antibody concentration and enzyme-labeled antibody concentration on target antigen detection. According to the average gray value measured under different N protein concentrations, the standard curve of the method was established and the sensitivity was tested, and its linear regression was obtained. The equation is y = 9.8286x+137.6, R2 = 0.9772 > 0.90, which shows a high degree of fit. When the concentration of coating antibody and enzyme-labeled antibody were 1 μg/mL and 2 μg/mL, P > 0.05, the difference was not statistically significant, so the lower concentration of 1 μg/mL was chosen as the coating antibody concentration. The results show that the minimum concentration of N protein that can be detected by this method is 8 μg/mL, and the minimum concentration of coating antibody and enzyme-labeled antibody is 1 μg/mL, which has the characteristics of high sensitivity and good repeatability.

Metal-Ion-Responsive Chromogenic Probe for Rapid, On-Location Detection of Foodborne Bacterial Pathogens in Contaminated Food Items

An amphiphilic chromogenic probe based on an oxidized di(indolyl)arylmethane backbone has been utilized for visual detection of both Cu²⁺ (detection limit = 8.5 ppb) and Hg²⁺ (detection limit = 10.2 ppb) ions via mutually independent sensing pathways. The Cu²⁺ ion binds to the carboxylate ends (donor site) and induces a color change from orange to yellow in the aqueous medium, while coordinating Hg²⁺ at the bisindolyl moiety (acceptor site) can result in the formation of a red-colored solution. Interestingly, by selecting the proper excitation channel, we can specifically excite either the monomer species or nanoaggregates. The addition of Hg²⁺ enhances the monomer fluorescence, while Cu²⁺ induces quenching. However, in both cases, metal-ion coordination triggers dissociation of a preformed self-assembled structure. Further, the in-situ-formed Cu(II) complex was utilized for rapid, on-location detection of food-borne pathogens, such as Escherichia coli (E. coli) in contaminated food items and water (detection limit = 52 CFU·mL^-1). E. coli induces reduction of Cu²⁺ to Cu⁺ and transforms the yellow-colored solution into an orange-colored solution. Finally, low-cost, reusable paper strips were designed as an eco-friendly, sustainable strategy to detect bacterial pathogens.