A simple and fast alternative colorimetric sensing platform for selective determination of vitamin B1 in urine samples was proposed.

A simple and novel transparency sheet-based colorimetric detection device using gold nanoparticles (AuNPs) modified by 4-Amino-6-hydroxy-2-mercaptopyrimidine monohydrate (AHMP) was fabricated and developed for the determination of calcium ions (Ca2+). The detection was based on a colorimetric reaction as a result of the aggregation of modified AuNPs induced by Ca2+ due to the ability to form strong electrostatic interactions between positively charged Ca2+ and negatively charged modified AuNPs. Probe solution changes color from red to blue in the presence of Ca2+ and can be observed by the naked eyes. To verify the complete self-assembly of the AHMP onto the AuNP surface, the modified AuNPs were characterized using ultraviolet–visible spectroscopy and zeta potential measurements. Under optimal conditions, a quantitative linearity was 10 to 100 ppm (R2 = 0.9877) with a detection limit of 3.05 ppm. The results obtained by the developed method were in good agreement with standard atomic absorption spectrometry (AAS) results and demonstrated that this method could reliably measure Ca2+. Overall, this novel alternative approach presents a low-cost, simple, sensitive, rapid, and promising device for the detection of Ca2+.