An RNA aptamer photoelectrochemical biosensor based on the exciton energy transfer constructed for theophylline detection

A novel photoelectrochemical (PEC) biosensor was developed incorporating a specifically designed RNA aptamer for the detection of theophylline (TP). This involved utilizing two nucleotide base aptamers with tailored sequences designed to target TP. The 3′ end of a single-stranded RNA sequence (5′-GGAUACCA–(CH₂)₆–SH-3′) and the 5′ end of a complementary stranded RNA sequence (5′–HS–(CH₂)₆-CCUUGGAAGCC-3′) were linked to gold nanoparticles (AuNPs) and CdS quantum dots (QDs), respectively. These two single-stranded RNAs (ssRNA) formed a double-stranded RNA (dsRNA) capable of recognizing TP. This major structural change altered the spacing between QDs and NPs, which signaled the presence and concentration of TP. TP was photoelectrochemical catalytic oxidation by the hole of CdS QDs under illumination, then anode photocurrent was generated. Due to the increase in surface impedance and the effect of exciton energy transfer (EET) between QDs and AuNPs, the photocurrent would undergo varying degrees of change. TP was detected by changes in photocurrent. PEC detection of TP was achieved in the range of 0.1 μM–200 μM. The detection limit was 0.033 μM. The method exhibited commendable reproducibility and remarkable selectivity. The biosensor was used to measure TP content in tea, beverages and blood samples, resulting in satisfactory recovery rates.