A homogeneous photoelectrochemical hydrogen sulfide sensor based on the electronic transfer mediated by tetrasulfophthalocyanine

Hydrogen sulfide (H2S) can regulate a variety of physiological functions, and the development of sensitive H2S detection methods is a requirement. In this study, a homogeneous photoelectrochemical (PEC) sensor for H2S detection was constructed based on the energy level matching of iron(III) phthalocyanine-4,4′,4′′,4′′′-tetrasulfonic acid ([Fe(III)PcS4]+) and n-GaN. The photocurrent of n-GaN could be suppressed by monomeric [Fe(III)PcS4]+ since the photogenerated electrons in the conduction band (CB) of n-GaN could be injected into the LUMO of [Fe(III)PcS4]+. Under weak alkaline conditions, monomeric [Fe(III)PcS4]+ can be converted to [Fe(I)PcS4]− after reacting with H2S with high selectivity. The LUMO of [Fe(I)PcS4]− was higher than the CB of n-GaN, so the photogenerated electrons in the LUMO of [Fe(I)PcS4]− could be injected back into the CB of n-GaN. The electron–hole pair recombination could be hindered, which resulted in the recovery of the system photocurrent. In the H2S concentration range of 10.0 nM–50.0 μM, a linear relationship was obtained between the photocurrent and the logarithm of H2S concentration with a detection limit of 3.40 nM. The proposed method avoids tedious electrode modifying procedures required in conventional PEC sensors and it was applied to detect extracellular H2S in rat brains coupled with microdialysis.