A ratiometric fluorescence method for detection of Fe3+ based on longer wavelength excitation luminescence of homovanillic acid

A novel luminescence phenomenon of homovanillic acid (HVA) that the excitation wavelength is longer than the emission wavelength (LExL, λ ex-L  > λ em ) was observed, which was monitored by using a common spectrofluorometer with a xenon lamp as an excitation light source. As the addition of Fe 3+ , the intrinsic fluorescence of HVA at 310 nm was obviously quenched and a new emission peak at 424 nm emerged and raised under 557 nm excitation. The similar emission spectra of HVA-Fe 3+ were also obtained at 287 nm excitation. Thus, a dual-mode ratiometric fluorescence (RF) method for detecting Fe 3+ was developed based on LExL and Stokes fluorescence (SF) of HVA. The RF signals of lg( I 424 nm / I 310 nm ) had excellent linearity with Fe 3+ concentration in the range of 0.50–100 μM. Their detection limits were 0.073 μM and 0.090 μM for the LExL and SF methods, respectively. The LExL and SF methods exhibited high selectivity for detecting Fe 3+ , and the former has stronger anti-interference ability to Cu 2+ , Fe 2+ etc. The proposed two methods were successfully applied for the determination of Fe 3+ in actual water samples. The interaction mechanism of HVA with Fe 3+ was also studied.