Biodegradable colorimetric sensor based on starch/Alizarin Red S for naked-eye detection of free formaldehyde content in hair care products

We present the construction of a biodegradable colorimetric sensor on the microtube lid for formaldehyde determination via naked-eye detection and /or UV–Vis spectrophotometry. Alizarin Red S (ARS) was subjected as the effective reagent for formaldehyde detection by incorporation in a thin film of starch. The sensor was accredited by the reaction of formaldehyde with ARS based on a color response from purple to yellow at pH ۱۲. The sensor characterization was obtained by Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscope (FE-SEM), and energy-dispersive X-ray (EDX) spectroscopy analytical methods. The effect of the main parameters on the detection of formaldehyde was studied and optimized. Under optimal conditions, the linearity range of colorimetric response was obtained in the concentration range of ۰.۱۵-۱۰ mg L−۱ with a determination coefficient (R۲) of ۰.۹۹۲۳. A limit of detection (LOD) of ۰.۰۵ mg L−۱ and a relative standard deviation (RSD, n=۵) of ۱.۲ % were achieved. This method presented a short response time (within ۱۵ min) for the application as biosensing. Subsequently, the concentrations of formaldehyde in hair care products (hair shampoo and conditioner samples) were successfully obtained with good recoveries.