TiO₂/g-C₃N₄/CdS Nanocomposite-Based Photoelectrochemical Biosensor for Ultrasensitive Evaluation of T4 Polynucleotide Kinase Activity

Abstract

Herein, an efficient photoelectrochemical (PEC) platform was constructed by a cosensitization strategy with a cascade energy level arrangement for the ultrasensitive evaluation of T4 polynucleotide kinase (T4 PNK). Based on CdSe quantum dots (QDs) with an extremely narrow bandgap, this cosensitization strategy offered a highly efficient sensitizer with a matching band-edge level of a ternary TiO2/g-C3N4/CdS nanocomposite. In this protocol, the ternary nanocomposite was first prepared to serve as the matrix to construct the PEC sensing platform. On the other hand, a well-designed hairpin DNA1 probe with 5′-hydroxyl termini was specifically phosphorylated by T4 PNK which would be selectively cleaved with lambda exonuclease (λ-Exo) outputting the 3′-thiol end ssDNA2. After tagged with CdSe QDs, ssDNA2 was captured by the complementary capture DNA3 on the electrode surface. As a result, CdSe QDs were in close contact with the ternary nanocomposite matrix, leading to an enhanced photocurrent response. Therefore, this proposed PEC platform displayed an analytical performance with a wide linear range from 0.0001 to 0.02 U mL–1 and a low detection limit down to 6.9 × 10–5 U mL–1. Moreover, this ternary nanocomposite-based platform exhibited excellent selectivity, good reproducibility, and remarkable storage stability, which shows great potential for T4 PNK detection and inhibitor screening.

Facile synthesis and photoelectrochemical properties of novel TiN/C3N4/CdS nanotube core/shell arrays

“…While generating photogenerated electrons, the photogenerated holes are left in the valence band of g-C3N4 and CdS, respectively. Because the valence band of g-C3N4 is more positive than that of CdS, the holes of the g-C3N4 valence band can easily move to the valence band of CdS [70][71][72]. Consequently, the composite of g-C3N4 and CdS deposited on TiN substrate can significantly enhance the photoelectrocatalytic performance due to the effective separation of electron-hole pairs and broadening of the light absorption range.…”

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)–Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

“…The rapidly increased photocurrent is detected in "trace b" (from 10 to 30 s) due to decrease in the rate of electron-hole recombination and the high-efficiency absorption. In the TiO2/g-C3N4 modified-FTO in "trace c", the photocurrent increases to 30.7 μA since the bandgap of the g-C3N4 reduces the charge carrier recombination and facilitates the electron transmission [557]. The photocurrent increases in "trace d" (TiO2/g-C3N4/CdS nanocomposite-modified electrode).…”

“…Like other applications, g-C 3 N 4 -TiO 2 based structures are one of the most used composites for sensing applications. Li et al demonstrated that the photoelectrochemical TiO 2 /g-C 3 N 4 /CdS platform could be employed for the ultrasensitive determination of T4 polynucleotide kinase (T4 PNK) because this composite showed significant stability and reproducibility with high selectivity [557]. The photocurrent response is demonstrated in Figure 21A.…”

“…The photocurrent increased to 80.0 µA after attaching DNA 3 , which can capture ssDNA 2 to the electrode and then blocking 6-mercaptohexanol (MCH) ("trace e"). For comparison, the photocurrent of CdSe QDs with or without the bio-functionalization of DNA 2 on the electrode matrix is 180 and 78 µA, respectively [557]. In addition, "trace f" shows that DNA 2 -CdSe QDs hybridized onto the surface, the photocurrent density increases to 180.0 µA since the presence of CdSe QDs improve the light absorption efficiency.…”

“…To compare, CdSe QDs also functionalized the electrode matrix without DNA 2 , and the result showed that the photocurrent density is about 78.0 µA which is similar to the "trace e" and highly lower than "trace f". As a result, the constructed platform shows a promising candidate for ultrasensitive detection of T4 PNK activity [557]. TiO 2 with g-C 3 N 4 is also used for sensitive detection of protein kinase A (PKA), which is an enzyme that covalently decorates proteins with phosphate groups [558].…”