Search

A gold nanoparticles (AuNPs) enhancement strategy for lateral flow immunoassays (LFIAs) was previously reported to improve assay sensitivity. The multi-steps of detection resulted in a tedious procedure. In this report, to reduce this limitation, a sequential flow LFIA was introduced to perform the AuNPs enhancement in only single step operation using C-reactive protein (CRP) as a model analyte. The delay and non-delay channels created on nitrocellulose membrane (NCM) using wax-printing method were used to deliver immunoassay and AuNPs enhancement reagents to the detection zone sequentially. For the enhancing step, AuNPs were enlarged by the catalytic reaction of KAuCl4 and NH2OH⋅HCl. Under optimal conditions, a calibration curve was found in a range of 0.1−5 μg⋅mL−1 with a good linear correlation (R2 = 0.9953). The limits of detection (LOD) were found to be 0.1 and 0.001 μg⋅mL-1 for naked eye observation and calculation (3SD/slope), respectively. Furthermore, the device shows no cross-reactivity with common interferences for CRP. The platform was successfully applied to detect CRP in certified human serum samples within 15 min, demonstrating the simplicity and speed of the AuNPs enhancement strategy platform. These promising results suggest that the new device may be used as an alternative tool for CRP detection and other biomarkers for POCT analysis.

A l -cysteine-modified silver nanoplate ( l -cys-AgNPl)-based colorimetric assay was developed for simple and rapid screening for copper (II) ions (Cu2+) in aqueous solution. The assay is based on the Cu2+-induced aggregation of l -cys-AgNPls. In the presence of Cu2+, l -cys-AgNPls were aggregated immediately and the color of solution was distinctly changed from violet to blue within 5 min. This method enabled the quantitative measurement of Cu2+ with sample volumes as low as 5 µL. Under optimized conditions, the limit of detection (LOD) was 1 ppm and 0.34 ppm by naked eye and smartphone with RGB application, respectively. For quantitative analysis, the calibration curve was constructed by plotting the differences in absorbance ratio at wavelengths of 620 nm and 570 nm (A620/A570) of sample and blank as a function of Cu2+ concentration. This assay detected Cu2+ in the range of 0.25 to 6 ppm (R2 = 0.9951) and the LOD was 0.22 ppm. In addition, l -cys-AgNPls exhibited good selectivity for Cu2+. Additionally, the developed method was successfully applied for rapid screening of Cu2+ in real wastewater samples with % recovery in the range of 73.08 to 114.62 and 93.48 to 114.04 by UV-visible spectrometry and smartphone with RGB application, respectively. The results from the developed method were compared with those from atomic absorption spectrometry and no significant difference was found between the two methods. The developed colorimetric method is promising for on-site detection of Cu2+ with high accuracy, good selectivity, and minimal reagent consumption.

The measurement of cortisol (stress hormone) is important for diagnosis and monitoring of stress-related diseases. A paper-based immunosensor with a competitive assay was developed for quick and easy detection of cortisol levels in serum. The paper-based sensor was fabricated using a simple and cheap wax printing method. Cortisol conjugated-BSA was immobilized on the paper's surface in the detection zone for the competitive immunoassay. Anti-cortisol mAb-conjugated gold nanoparticles, as signal indicator, were used to detect cortisol in the sample. A 2-step procedure included applying the sample and washing for cortisol determination. The results showed that the device had the ability to differentiate cortisol levels into three ranges:25 μg/dL, 25-50 μg/dL and50 μg/dL by visual detection. The limit of detection determined by an image processing program was 21.5 μg/dL. This assay was successfully developed to detect cortisol in serum, and showed good recovery and precision. Our results correlated well with those obtained using an electrochemiluminescence method. This paper-based immunosensor provided a rapid and simple screening test for serum cortisol detection.

In the expression of bioaccumulated elemental mercury (Hg 0) toxicity, the first Hg 0 oxidation step is crucial. Therefore, to clarify the mechanism underlying the interactions of sulfhydryl (SH) compounds and Hg 0 in the present study, we analyzed the oxidation of reduced glutathione (GSH) and L-cysteine (Cys) in the presence of Hg 0 in aqueous solution by cyclic voltammetry (CV). Production of Hg2+ in the reaction mixture was found to increase along with a decrease in free SH residues. CV showed that the oxidation of Cys increased after a 4-h incubation in the presence of Hg(0), but the oxidation of Cys after a 24-h incubation was suppressed. Conversely, GSH oxidation increased with incubation time in the absence of Hg(0). In the presence of Hg(0), the oxidation of GSH was suppressed. The different reactivities of Cys and GSH with Hg(0) may arise from differences in their oxidation/reduction potentials and pH. The important SH compound interactions with Hg(0) oxidation were as follows: (i) oxidation of Hg(0) to form either mercurous ion (Hg+) or mercuric ion (Hg2+) which both form stable complexes in aqueous solution as Hg I (RS) or Hg II(RS)2; (ii) catalyzed oxidation of SH compounds in the presence of Hg 0; and (iii) suppression of the oxidation of SH compounds due to the reduced concentration of free SH compounds through the binding of SH compounds with Hg+ or Hg2+ The present results demonstrate the chemical reaction processes by which Hg 0 dissolves in aqueous solution in the presence of SH compounds, and contribute to our understanding of SH compounds in non-enzymatic Hg 0 oxidation in vivo.