Elsevier

Analytica Chimica Acta

Volume 943, 2 November 2016, Pages 106-113
Analytica Chimica Acta

Resonance energy transfer between ZnCdHgSe quantum dots and gold nanorods enhancing photoelectrochemical immunosensing of prostate specific antigen

https://doi.org/10.1016/j.aca.2016.09.015Get rights and content

Highlights

  • Nanocomposites based on AuNRs integration with ZnCdHgSe QDs were synthesized.

  • The photocurrent response of ZnCdHgSe QDs was improved by resonance energy transfer.

  • A photoelectrochemical immunosensor was developed for PSA.

  • Highly sensitive and selective determination of PSA was confirmed.

Abstract

Gold nanorods (AuNRs) integrated with ZnCdHgSe near-infrared quantum dots (AuNRs-ZnCdHgSe QDs) were successfully synthesized and characterized by transmission electron microscope, X-ray photoelectron spectroscopy, and X-ray diffraction. A glassy carbon electrode was decorated with the aforementioned AuNRs-ZnCdHgSe QDs nanocomposite, which provides a biocompatible interface for the subsequent immobilization of prostate specific antibody (anti-PSA). After being successively treated with glutaraldehyde vapor and bovine serum albumin solution, a photoelectrochemical immunosensing platform based on anti-PSA/AuNRs-ZnCdHgSe QDs/GCE was established. The photocurrent response of ZnCdHgSe QDs was tremendously improved by AuNRs due to the effect of resonance energy transfer which can be deduced from the dependence of the enhanced efficiency on the AuNRs with different length-to-diameter ratios and spectral absorption characteristics. A maximum photocurrent was obtained when the absorption spectrum of AuNRs matched well with the emission spectrum of ZnCdHgSe QDs. A photoelectrochemical immunosensor for prostate specific antigen (PSA) was achieved by monitoring the photocurrent variation. The photocurrent variation before and after being interacted with PSA solution exhibits a good linear relationship with the logarithm of its concentration (logcPSA) in the range from 1.0 pg mL−1 to 50.0 ng mL−1. The detection limit of this photoelectrochemical immunosensor is able to reach 0.1 pg mL−1 (S/N = 3). Determining PSA in clinical human serum was also demonstrated by using the developed anti-PSA(BSA)/AuNRs-ZnCdHgSe QDs/GCE electrode. The results were comparable with those obtained from an enzyme-linked immunosorbent assay method.

Introduction

Photoelectrochemical technique has become a newly developed approach for the fabrication of biosensors [1], [2]. The merits of the photoelectrochemical sensing system, such as simple apparatus, low cost, and facile fabrication, are inherited from the superior properties of electrochemical and photochemical sensing techniques [3]. Due to the complete separation of the excitation source from the detection signal, the background signal can be subtracted, thus leading to high sensitivity and excellent sensing performance [4], [5], [6]. Thus, photoelectrochemical approaches are most pertinent to become a sensing platform for biomacromolecules at ultralow concentration, especially for DNA, RNA, and proteins [7], [8], [9], [10]. In this technique, the photocurrent generated by the specific recognition, steric-hindrance effect, enzymatic reaction, and energy transfer is used as the detection signal for quantitative analysis of biomolecules [11].

Energy transfer has been demonstrated to be a suitable candidate for the sensitive determination of biomolecules by improving the charge dissociation and transport efficiency [12], [13], [14]. In a photoelectrochemical sensing system, energy transfer typically involves a non-radiative transfer process in which the excitation energy is transferred from an excited donor to a proximal acceptor [15]. Energy transfer is a consequence of a long-range dipole-dipole interaction between the donors and the acceptors. It is extremely dependent on the donor-acceptor distance and their relative dipole orientations. The overlap of the spectral band between the donor and the acceptor (>30%) and the mutual distance (<10 nm) are crucial factors for effective energy transfer [16]. Semiconductors are commonly used as donors to produce excitation resource. Among them, quantum dots are considered to be the prominent candidates for photoactive materials due to their fascinating characteristics such as excellent photostability, broad excitation spectral range, adjustable emission wavelength, and superior biocompatibility. Unfortunately, some of the quantum dots (ZnS, CdS etc.) possess large band gap and thus require high-energy excitation light sources to produce photocurrent [17]. They often encounter many difficulties such as photocorrosion under illumination, deactivating biomolecules and low photoelectrochemical conversation efficiency, thus leading to instability, poor sensitivity, and selectivity for biosensing.

In order to overcome these challenges, some semiconductors possessing narrow band gap were successfully developed [18], [19], [20]. They can be excited by a long wavelength light source, preventing damage to biomaterials and improving the photoelectrochemical sensing performance towards target molecules. Among them, near-infrared (NIR) emitting QDs have been considered as the suitable candidates for biosensing, bioimaging, and photoelectrochemical determination. Recently, quaternary ZnCdHgSe QDs are successfully synthesized in our group and have been demonstrated their capability of being effectively excited at 690 nm [21]. Although sensitive photoelectrochemical response can be obtained by layer-by-layer assembling ZnCdHgSe QDs and polymerized ionic liquid film, an effective method for enhancing the photocurrent response under visible or near IR illumination is desirable for fabricating a biosensing system based on ZnCdHgSe QDs. Energy transfer can be an excellent approach to enhance the photoelectric conversion efficiency by improving the electron-hole pair separation efficiency. Noble metal nanomaterials, especially gold, are well-known to be good energy acceptors due to their unique features, such as surface plasmon resonance, high extinction coefficient and broad absorption spectra [22], [23], [24]. Therefore, gold nanorods (AuNRs) were employed as acceptors to enhance the photocurrent response of ZnCdHgSe QDs generated from the effects of energy transfer and high conductivity. In an energy-transfer based photo- or photoelectrochemical sensing system, the spectral matching of the donor and the acceptor is a crucial element to influence the intensity of photocurrent. Thus, gold nanorods with different morphological characteristics were fabricated to investigate the effects of the absorbance properties of gold nanorods on the photocurrent response of ZnCdHgSe QDs.

To evaluate the photoelectrochemical sensing performance of AuNRs/ZnCdHgSe QDs nanocomposites, anti-human PSA monoclonal antibody (anti-PSA) was selected as a model protein to develop a biosensing system. Gold nanorods not only supplied some active sites to anchor anti-PSA onto the photoelectrochemical platform, but also exhibited some excellent properties to improve the photocurrent response. As the maximal absorption wavelength of gold nanorods is matched well with the maximal emission wavelength of ZnCdHgSe QDs, the maximum photocurrent response can be produced. When the specific immunoreaction between the anti-PSA and PSA was performed, the blocking effect of PSA on the mass- and electron transfer of ascorbic acid will cause the photocurrent response decreasing. The variation of photocurrent response was used for the quantitative assay of PSA concentration. All stepwise processes for the AuNRs/ZnCdHgSe QDs preparation and the PSA immunosensor fabrication were thoroughly characterized with transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical techniques. The photoelectrochemical sensing performances of the AuNRs/ZnCdHgSe QDs based biosensor towards PSA were evaluated. The practical application of the as-prepared biosensor was also demonstrated by determining PSA concentration in real clinical serum samples.

Section snippets

Materials

N-acetyl-l-cysteine (NAC) was bought from Aladdin Reagent Inc. (Shanghai, China). Cetyl trimethyl ammonium bromide (CTAB), bovine serum albumin (BSA), selenium powder, NaBH4, HAuCl4, ZnCl2, glutaraldehyde and ascorbic acid (AA) were supplied by Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). CdCl2·2.5H2O were bought from Chengdu Chemical Reagent Plant (Chengdu, China). HgCl2 was supplied by Beijing Chemical Reagent Company (Beijing, China). Mouse anti-human PSA monoclonal antibody

Results and discussion

Synthesized gold nanorods and ZnCdHgSe QDs were characterized by various techniques. Fig. 1 (A) presents the transmission electron microscopic images of gold nanorods prepared by controlling the reaction time at 15 h (a), 20 h (b) and 24 h (c). It was obvious to see that the morphology of the as-synthesized gold nanorods was rod-like nanoparticles. The length-to-diameter ratio of gold nanorods was increased with the reaction time prolonging. UV–Vis absorption spectrum of these gold nanorods

Conclusions

A novel photoelectrochemical immunosensor for PSA was fabricated by using AuNRs/ZnCdHgSe QDs nanocomposites as photoelectric conversion materials and anti-PSA as the receptor. It is interesting to note that the morphological characteristics of AuNRs exhibit a significant influence on the photocurrent response of ZnCdHgSe QDs. AuNRs not only supplied some active sites for anti-PSA immobilizing, but also played an important role as an acceptor in improving the electron-hole pair separation

Acknowledgements

The authors gratefully acknowledge the financial supports from The National Natural Science Foundation of China (No. 21275166 and 21675175) and The Natural Science Foundation of Hubei Province (No.2015CFA092).

The first two authors contributed equally to this work.

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