Detection of Waterborne and Airborne Formaldehyde: From Amperometric Chemosensing to a Visual Biosensor Based on Alcohol Oxidase

Abstract

A laboratory prototype of a microcomputer-based analyzer was developed for quantitative determination of formaldehyde in liquid samples, based on catalytic chemosensing elements. It was shown that selectivity for the target analyte could be increased by modulating the working electrode potential. Analytical parameters of three variants of the amperometric analyzer that differed in the chemical structure/configuration of the working electrode were studied. The constructed analyzer was tested on wastewater solutions that contained formaldehyde. A simple low-cost biosensor was developed for semi-quantitative detection of airborne formaldehyde in concentrations exceeding the threshold level. This biosensor is based on a change in the color of a solution that contains a mixture of alcohol oxidase from the yeast Hansenula polymorpha, horseradish peroxidase and a chromogen, following exposure to airborne formaldehyde. The solution is enclosed within a membrane device, which is permeable to formaldehyde vapors. The most efficient and sensitive biosensor for detecting formaldehyde was the one that contained alcohol oxidase with an activity of 1.2 U·mL^-1. The biosensor requires no special instrumentation and enables rapid visual detection of airborne formaldehyde at concentrations, which are hazardous to human health.

Keywords: Hansenula polymorpha; biosensor, alcohol oxidase; chemosensing electrode; formaldehyde; microcomputer-based analyzer.

Figure 1.

(a) Block diagram of the MC; and (b) Photograph of the chemosensor-based analyzer.

Figure 2.

Amperometric response of the chemosensor based on a 3.05 mm rod platinized carbon electrode for various analytes at different working potentials: +250 mV, +50 mV, 0 mV vs. Ag/AgCl (20 mM analyte in 20 mM phosphate buffer (PB), pH 7.5).

Figure 3.

(a) Linearity test for the amperometric response of the 3.05 mm rod Pt-carbon electrode and 4 mm planar Pt-carbon electrode DRP-150 to FA; (b) Conditions: working potential 0 mV vs. Ag/AgCl, 20 mM PB, pH 7.5. Slopes of the lines (as sensitivity characteristics) and R (linear regression coefficients) are shown in the inserts.

Figure 4.

Amperometric determination of formaldehyde in a wastewater sample using a 4 mm planar Pt-gold electrode DRP-C220AT. Conditions: working potential 0 mV vs. Ag/AgCl, 20 mM PB, pH 7.5. Parameters of the line (“A” and “B”) are shown in the inserts: “A”—corresponds to the signal of the analyzed sample without addition of a FA standard, “B”—slope of the calibration curve, and “R”—linear regression coefficient, “n”—dilution of the tested sample. The calibration curve was obtained by adding aliquots of a FA standard solution to the analyzed sample.

Figure 5.

Color development in the membrane devices containing 3.5 mg·mL⁻¹ of HRP, 2 mg·mL⁻¹ of chromogen and 5 or 10 U·mL⁻¹ of AOX. The devices were exposed to airborne FA at a concentration of 0.3 ppm, and the color intensity was measured at various time periods starting from the color development point.

Figure 6.

Time of color development in the membrane devices containing HRP—3.5 mg·mL⁻¹, chromogen—2 mg·mL⁻¹ and AOX—2.5 U·mL⁻¹. The devices were exposed to airborne FA at various concentrations and the reaction time was registered.

Figure 7.

Time of color development in the membrane devices containing 3.5 mg·mL⁻¹ of HRP, 2 mg·mL⁻¹ of chromogen and various concentrations of AOX. The devices were exposed to airborne FA at various concentrations, and the reaction time was registered.