Alkaline phosphatase (ALP) is a significant biomarker in clinical diagnostics, and the abnormal level of ALP enzyme in serum is closely related to various diseases such as bone or liver cancer, bone metastases, and extrahepatic biliary obstruction. Herein a simple and portable photothermal biosensor was developed for sensitive detection of ALP enzyme based on the formation of polydopamine (PDA) nanoparticles using a thermometer or temperature discoloration sticker as readout. A MnO2 nanosheet was first prepared using a novel one-pot strategy which was operationally simple and not overly time-consuming. Then dopamine (DA) was quickly polymerized into PDA nanoparticles in the presence of the MnO2 nanosheet. When the model analyte ALP was present, the substrate 2-phospho-l-ascorbic acid trisodium salt (AAP) was catalytically hydrolyzed into l-ascorbic acid (AA), resulting in the inhibition of the formation of the PDA nanoparticles owing to the fact that the MnO2 nanosheet was reduced to Mn2+ by the generated AA. Thus, a portable biosensor based on the photothermal properties of PDA nanoparticles for ALP enzyme detection was established with a detection limit as low as 0.1 U/L (thermometer) and 1 U/L (temperature discoloration sticker). In addition, it also showed excellent sensing performance for the ALP assay in human serum. Such a simple, label-free, cost-effective, and sensitive assay could exhibit real potential application for ALP detection and early diagnosis, especially in developing countries or remote regions.

No abstract

Developing a strategy of modulating β-amyloid (Aβ) aggregation with low cost, easy synthesis, high efficiency, and biosafety is significant and a challenge for Alzheimer’s disease (AD) therapy. Herein, DNA aptamer (Aβ-Apt) against Aβ42 obtained by in vitro selection was developed as a potent inhibitor of Aβ42 aggregation for the first time. Indeed, the Aβ42 monomer fibrillation was inhibited completely by Aβ-Apt. Notably, the inhibition effect of Aβ-Apt on the Aβ42 oligomer aggregation was more obvious than that on the Aβ42 monomer aggregation. It was presumed that the distinguishing effect may be attributed to different binding behaviors of Aβ-Apt with Aβ42 monomer and Aβ42 oligomer. Surface plasmon resonance analysis demonstrated that Aβ-Apt specifically recognized Aβ42 monomer and Aβ42 oligomer. Furthermore, the binding affinity of Aβ-Apt with Aβ42 oligomer was larger than that of Aβ-Apt with Aβ42 monomer. This work provided a promising platform with high efficiency for manipulating Aβ aggregation.

The exhaustive investigating interactions between recognition probes and amyloid aggregates, especially simultaneous recognition events, are challenging and crucial for the design of biosensing probes and further diagnosis of amyloid diseases. In the present work, the interactions of aptamers (Apts) with β-amyloid (Aβ) aggregates were explored thoroughly by single-molecule force spectroscopy (SMFS). Indeed, it was found that the interaction of aptamer1 (Apt1)−amyloid aggregates was different from that of aptamer2 ( Apt2)−Aβ 40 aggregates at the single-molecule level. Especially, the interaction force of Apt1−Aβ 40 fibril showed a double distinguishing Gaussian fitting. The only unimodal distribution of the force histogram was displayed for the interactions of Apt2−Aβ 40 oligomer, Apt2−Aβ 40 fibril, and Apt1−Aβ 40 oligomer. More intriguingly, two Apts could bind to amyloid aggregates simultaneously.With the assistance of two Apts recognition, a novel sensitive dual Apt-based surface plasmon resonance (SPR) sensor using Au nanoparticles (AuNPs) was developed for quantifying Aβ 40 aggregates. The dual Apt-based SPR sensor not only avoided the limitation of steric hindrance and epitope but also employed simple operation as well as inexpensive recognition probes. A detection limit as low as 0.2 pM for Aβ 40 oligomer and 0.05 pM for Aβ 40 fibril could be achieved. Moreover, the established sensor could be successfully applied to detect Aβ 40 aggregates in artificial cerebrospinal fluid (CSF) and undiluted real CSF. This work could provide a strategy to monitor a simultaneous recognition event using SMFS and broaden the application of Apts in the diagnosis of neurodegenerative diseases.

The real application of DNA-functionalized gold nanoparticles (DNA-Au NPs) was limited by decreased stability and irreversible aggregation in high-ionic strength solutions and complex systems. Therefore, exploring a kind of DNA-Au NPs with excellent stability in high-ionic strength solutions and complex systems is challenging and significant. Herein, a novel universal bioconjugate strategy for constructing ultrastable DNA-Au NPs was designed based on the combination of polydopamine (PDA) shell and DNA linker. The obtained DNA-linked Au@polydopamine nanoparticles (DNA-Au@PDA NPs) showed colloidal stability in high-ionic strength solution and complex systems (such as human serum and cell culture supernatant). Moreover, the nanoparticles still maintained good dispersion after multiple freeze–thaw cycles. The high stability of DNA-Au@PDA NPs may be attributed to increasing the electrostatic and steric repulsions among nanoparticles through the effect of both PDA shell and DNA linker on Au@PDA NPs. For investigating the application of such nanoparticles, a highly sensitive assay for miRNA 141 detection was developed using DNA-Au@PDA NPs coupled with dynamic light scattering (DLS). Comparing with the regular DNA-Au NPs, DNA-Au@PDA NPs could detect as low as 50 pM miRNA 141 even in human whole serum. Taken together, the features of Bio/Nanointerface make the nanoparticle suitable for various applications in harsh biological and environmental conditions due to the stability. This work may provide a universal modification method for obtaining stable nanoparticles.