A smartphone-assisted colorimetric test kit for the determination of indole-3-carbinol in dietary supplements

Abstract

This work introduces a sol-gel test kit for the colorimetric determination of indole-3-carbinol (I3C) in dietary supplements sold in health food, pharmacies, and online sources. The test kit comprises a chromogenic reagent of para-dimethylaminocinnamaldehyde (DMACA) entrapped within a sol-gel matrix. The assay relies on the reaction of indole-3-carbinol with DMACA under acidic conditions to form a dark red-violet azafulvenium salt. Color changes are clearly visible to the naked eye and are evaluated with a smartphone application. Under optimized conditions, the method demonstrated a linear calibration range of 10–100 mg L^–1 (r² = 0.9892), with detection and quantification limits of 2.0 mg L⁻¹ and 6.7 mgL^–1, respectively. The smartphone-assisted colorimetric method showed good intra- and inter-day precision, with % RSDs lower than 8.1 %, and good accuracy, with acceptable relative errors in the range of 12.9–13.8 %. The sol-gel test kit showed long-term storage stability for two months at −18°C. For the analysis of ten dietary supplement products, smartphone-assisted colorimetric test kit is in good agreement with high-performance liquid chromatography with an ultraviolet detector (HPLC-UV) as reference method. This low-cost, portable and disposable test kit offers as an alternative approach for monitoring the quality of indole-3-carbinol dietary supplement.