LAUSR

Abstract Formaldehyde (FA) has been regarded as one of the most widespread chemical pollutants and severely threats human health. However, specific detection of FA in weakly acidic conditions using small-molecule based probe still remains a challenge. Herein, we reported a two-step responsive colorimetric probe based on heptamethine cyanine derivative (HCy1) for the detection of FA in weakly acidic environment. pH responsive piperazine moiety and FA responsive primary amine moiety were introduced to HCy1 simultaneously for achieving the two-step response. When exposed to FA, HCy1 exhibits obvious color change from blue to green in weakly acidic environment (pH 3–6) while stays as blue in neutral or basic environment. The color changing process was caused by two-step response of HCy1, namely, FA condensation-induced pKa increase and subsequent protonation under weak acidity. Besides, HCy1 exhibited short response time (within 30 s) and high sensitivity (detection limit of 3.25 μM) and selectivity to FA. The test paper based on HCy1 successfully achieved fast detection of FA in weakly acidic solution and gaseous environment. HCy1 is facile and effective for FA detection in weakly acidic conditions.