Dye-semiconductor Nanomaterials Based Photoelectrochemical Biosensing For Biothiol Detection

Biothiols such as cysteine and glutathione are one kind of small biomolecules involved in many important physiological reactions. Abnormal levels of biothiols have close relationship to many serious diseases, so the detection of biothiols is important for the early diagnostics of many diseases as well as unraveling the complex mechanism of physiological process. Although many methods including electrochemical biosensor and fluorescent probe based methods have been employed to the detection of biothiol, due to their structure similarity, the discrimination of one biothiol from other thiols is still a great challenge. Motivated by this, in this thesis, we developed two novel photoelectrochemical (PEC) methods which can perform cysteine or glutathione detection with both high sensitivity and good selectivity. The detailed information of this thesis was listed as follows:1、Photoelectrochemical biosensing of glutathione based on triphenylamine functional dye and TiO2(TCA-TiO2) nanocompositesIn this chapter, a novel triphenylamine functional dye (TCA for short) was synthesized and coupled with TiO2nanoparticle for the construction of PEC biosensing platform and the sensitive and selective detection of glutathione. In comparison to other functional dyes, the TCA with a non-planar structure could be well dispersed on the surface of TiO2nanoparticles, thus leading to obviously increased photoelectron transfer efficiency. When the TCA-TiO2nanocomposite was modified on the FTO electrode and employed for the detection of glutathione (GSH), a typical biothiol in our body, it showed a wide linear range (0.05to2.4mM) and an acceptable limit of detection (5.73μM) at a much lower detection potential of-0.3V, which was beneficial for excluding the interferences from other reducing agents existed in human bodies.2、Photoelectrochemical biosensing of cysteine based on triphenylamine modified TiO2(TTA-TiO2)In this chapter, a novel triphenylamine functional dye (TTA for short) with both high visible light harvest capacity and good cysteine discrimination ability was syntheisized and coupled with TiO2nanoparticle for the construction of highly selective cysteine PEC sensing platform. The TTA functional dye with a large π-conjugated system was composed of three parts, a triphenylamine group as a highly efficient visible light harvest capacity, a thiophene group as an electron transfer conductor, and a α,β unsaturated ketone as a cysteine identification group. In the absence of cysteine, due to the large π-conjugated system, suitable energy level, and good PEC transfer ability of TTA, it could highly efficient transfer photoelectron to the TiO2nanoparticle modified FTO electrode with the help of ascorbic acid as an electron sacrificing reagent and yield a high PEC current. In the presence of cysteine, the α,β unsaturated ketone of TTA could rapidly react with cysteine via a well known1,4addition reaction. In this case, the π-conjugated system of TTA was destroyed the PEC transfer pathway was blocked, resulting in a significantly decreased PEC current. Based on this PEC current decrease, which has a good linear relationship to the concentration of cysteine, the concentration of cysteine could be accuratedly quantified. Since the detection of cysteine is based on the specific interaction between cysteine and the TTA, the TTA based PEC sensor performed much better selectivity related to other biothiol PEC sensors. It could exclude the interfences from the19kinds of natural amio acids, the normal reducing reagents, and the other kinds of biothiols such as GSH and homocystine as well. In addition, the TTA-TiO2/FTO biosensor showed an acceptable linear range (1μM to0.1mM) and a low limit of detection of0.17μM, thus may have potential to be applied for the in-vivo detection of cysteine.