A label-free RTP sensor based on aptamer/quantum dot nanocomposites for cytochrome c detection

Abstract

Given the outstanding room-temperature phosphorescence (RTP) of Mn-ZnS quantum dots (QDs) and the specific recognition performance of the aptamer, we built phosphorescent composites from aptamers conjugated with polyethyleneimine quantum dots (PEI-QDs) and applied them to cytochrome c (Cyt c) detection. Specifically, QDs/CBA composites were generated from the electrostatic interaction between the positively-charged PEI-QDs and the negatively-charged Cyt c binding aptamer (CBA). With the presence of Cyt c, the Cyt c can specifically bind with the QDs/CBA composites, and quench the RTP of QDs through photoinduced electron-transfer (PIET). Thereby, an optical biosensor for Cyt c detection was built, which had a detection range of 0.166-9.96 μM and a detection limit of 0.084 μM. This aptamer-mediated phosphorescent sensor with high specificity and operational simplicity can effectively avoid the interference of scattering light from complex substrates. Our findings offer a new clue for building biosensors based on QDs and aptamers.

Fig. 1. Schematic illustration of fabricating of QDs/CBA nanocomposites for Cyt c detection.

Fig. 2. (A) The absorption (a) and RTP emission (b) spectra of PEI-capped Mn–ZnS QDs, inset: schematic illustration of electronic transition involved in the RTP emission from PEI-QDs; (B) UV/Vis spectra of PEI-QDs and QDs/CBA; (C) RTP emission spectra of PEI-QDs and QDs/CBA; (D) RTP emission spectra of the QDs/CBA stored at 4 °C for 1 month.

Fig. 3. (A) RTP emission spectra of QDs, QDs/CBA, QDs + Cyt c QDs/CBA + Cyt c; (B) RLS spectra of the QDs/CBA in the presence of different concentrations of Cyt c; (C) the zeta potential histogram of QDs, QDs/CBA, QDs/CBA/Cyt c; (D) combination mode diagram for Cyt c and CBA.

Fig. 4. (A) The RTP emission spectra of QDs/CBA in the presence of different concentrations of Cyt c (0, 0.166, 0.332, 0.83, 1.66, 3.32, 4.98, 6.64, 8.30, 9.96 μM); the inset photographs illustrate the RTP, QDs/CBA, QDs/CBA + Cyt c under UV light; (B) the linear relationship between the RTP intensity ratio P₀/P of QDs/CBA and Cyt c concentration.

Fig. 5. Effects of 1 × 10⁻⁶ mol L⁻¹ BSA, 1 × 10⁻⁶ mol L⁻¹ HAS, 50 U L⁻¹ ALP, 1 × 10⁻⁶ mol L⁻¹ IFN-γ and 9.96 μM Cyt c on the RTP intensity of QDs/CBA composites.