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

Abstract

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.