Cancer refers to disease that involves abnormal cell growth and may affect various parts of the body. Prostate cancer is one of the main cancer types which will be harmful to the health. Prostate-specific antigen (PSA) is a single-chain polypeptide containing 237 amino acids and is the most sensitive biomarker for prostate cancer [1–3]. Therefore, it is an urgent and important task to develop biomarkers for detecting prostate cancer with higher sensitivity. So far, a variety of analytical techniques have been used to detect PSA, such as radioimmunoassay, mass spectrometry immunoassay, enzyme-linked immunosorbent assay, colorimetric analysis, electrochemical methods, polymerase chain reaction and surface enhancement Raman analysis [4–9]. However, these methods require expensive apparatus and complicated pretreatment procedures. Determination process with facile steps would be warmly welcome. From last decade, fluorescence-based technology has attracted widespread attention due to its high sensitivity, simplicity and stability [10–12]. As for the structure, 2D materials have generated significant interests in biological applications due to their unique properties such as large surface area, bio-compatibility, and low toxicity [13–15]. In particular, 2D nanosheets have been provided as the excellent platforms for the detection of DNA sequence. As a result, a variety of 2D nanosheets, including transition metal dichalcogenide, metal oxides, and carbon nanomaterials, have been developed to construct nano-fluorescence sensor for the DNA detection [16–20]. Therefore, in our present study, we employed a highly sensitive two-dimensional CoOOH nanosheets based PSA sensor via the transduction of optical signals and CoOOH NSs were played as the host for the sensing process.
The cobalt oxyhydroxide nanosheet has been developed as a novel transition metal-based oxide nanomaterial with regular hexagon and rigid two-dimensional structure [21–23]. Therefore, the structure possesses similar features as some reported 2D nanosheets, such as graphene oxide (GO), MoS2, WS2, MnO2 and so on [24–28]. Most of them have been extensively used for biological applications owing to their quantum size properties and surface effects. Some of them were functionalized as powerful quenchers not only for organic fluorescent dyes but also for some fluorescent nanoparticles such as up-conversion nanoparticles and quantum dots [29, 30]. Because of the quantities of hydroxyls on the CoOOH NSs surface, CoOOH NSs gave rise to excellent water solubility, good biocompatibility and large specific surface area, which would contribute to the potential uses in environmental or biological conditions [31, 32]. To our knowledge, the employment of CoOOH NSs as the biosensor platform for the detection of PSA has not been reported.
Herein, CoOOH NSs were used as the signal substrate and its microstructure was verified. It has been found that CoOOH NSs can selectively adsorb fluorescent dye FAM-labeled aptamers (PA) and act as an efficient fluorescent dye quencher. The binding of the aptamer to the target PSA induced a rigid aptamer structure which significantly changed the integration process with the CoOOH NSs. Accordingly, such recognition resulted in the release of the aptamer PA from the nanosheet surface and restored the quenched fluorescence (Scheme 1). Therefore, the assay could be considered as direct, simple, sensitive, selective and suitable for PSA detection. It can be expected that the CoOOH NSs nano-host strategy would provide possibility in the field of early clinical diagnosis.