Colorimetric sensors for formaldehyde detection and electrochemiluminescent for pathogens detection

Abstract

In this work, two methods for the detection of formaldehyde and one assay for detection of Cryptosporidium parvum DNA (C. parvum) in water samples were developed. For the detection of formaldehyde, silver-doped hydroxyapatite (Ag-HAP) was used to extract formaldehyde from high volume samples and the Tollens’ reaction occurred on the solid surface. After the reaction, silver nanoparticles were produced on the material resulting in the material color change from off-white to yellow or brown depending on the concentration of formaldehyde. By using the Ag-HAP, the detection of formaldehyde was achieved by measuring the color intensity. Under the optimized conditions, this method has a linear range of 15-200 µg L-1 with the lowest concentration for detection of 15 µg L-1. The recovery of formaldehyde in sample observed by the proposed method was 86-111% with relative standard deviation less than 8%. For another formaldehyde detection, the agar-HPMC gel modified with Schiff’s reagent was used to detect formaldehyde in water samples. The detection of formaldehyde was based on Schiff’s reaction on the gel surface. The magenta color product could be observed on the Schiff-gel after the contact with formaldehyde solution. The color intensity of the gel measured by Image-J software depended on the concentration of formaldehyde. Under the optimized conditions, the linear range was observed from 2.00-10.00 mg L-1 with the limit of detection was 1.49 mg L-1. The recovery of formaldehyde in sample observed by the proposed method was 81-122% with the relative standard deviation less than 16%. For the detection of C. parvum DNA, the sandwich hybridization assay coupled with electrochemiluminescence measurement was designed and optimized. The detection of C. parvum DNA was based on the specific binding of capture DNA on magnetic beads and C. parvum DNA and the signal was amplified using liposomes containing Tris(2,2'-bipyridine) ruthenium(II) (Ru(bpy)32+) as reporter probe. Under the optimized conditions, the one-step, and three-step assay by using the hybridization buffer gave the high signal intensity with limit of detection of 0.039 nmol L-1 and 0.045 nmol L-1, respectively. This assay was further investigated in the microfluidic chip.