Colorimetric and fluorescence dual-signal sensing of L-Arginine based on TSPP-TA

L-Arginine (L-Arg) is an essential basic amino acid for human growth and development. Several health disorders can be caused when the level of L-Arg is too high or weak in the body of a human being. Therefore, the quantification of L-Arg is great importance in the field of life sciences. Based on this, 5,10,15,20-(4-sulphonatophenyl)porphyrin (TSPP) probes with excellent water solubility and high quantum yield were synthesized by one-pot method. It was applied to colorimetric and fluorescence sensing systems. The maximum fluorescence emission wavelength was obtained at 643 nm when the excitation wavelength was set at 515 nm. The fluorescence signal was "ON" state with the purple-red of TSPP solution. The introduction of tannic acid (TA) into the TSPP solution partially converted TSPP to the double protonated form (H₂TPPS^4-). In the reaction, electron transfer taken place, leading to a decrease in the absorbance and fluorescence emission intensity of TSPP. This resulted in a color shift of the solution from purplish-red to green, effectively turning the fluorescence signal to an "OFF" state. The absorbance and fluorescence emission intensity of the quenched TSPP were significantly recovered due to the acid-base neutralization reaction occurs between alkaline L-Arg and TA when L-Arg was added to the TSPP-TA dual-signal sensing system. The color of the solution transitioned from green to colorless. Concurrently, the fluorescence signal was activated, marking an "ON" state. Therefore, an "ON-OFF-ON" type colorimetric and fluorescence dual-signal sensing system was constructed with TSPP-TA/L-Arg. The results showed that the linear range of L-Arg in the colorimetric sensing was 3.14 μM-145.20 μM with the detection limit (LOD, S/N = 3) of 0.11 μM. In the fluorescent sensing system, the linear range of L-Arg was 1.49 μM-271.74 μM with the detection limit (LOD, S/N = 3) of 0.07 μM. This dual-signal sensing system, which combined colorimetric and fluorescence indicators, has been effectively utilized for the high-precision and sensitive detection of L-Arg in real-world samples.