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A large-size Bi2Se3 tape electrode (BTE) was prepared by peeling off a 2 × 1 × 0.5 cm high-quality single crystal. The feasibility of using the flexible BTE as an efficient bioplatform to load Au nanoparticles and probe DNA for HIV-1 DNA electrochemical sensing was explored. Differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) show that the resultant biosensor has a wide linear range from 0.1 fM to 1 pM, a low detection limit of 50 aM, excellent selectivity, reproducibility and stability, and is superior to the pM DNA detection level of Pt-Au, graphene-AuNPs hybrid biosensors. This outstanding performance is attributed to the intrinsic surface state of Bi2Se3 topological insulator in facilitating electron transfer. Therefore, BTE electrochemical biosensor platform has great potential in the application for sensitive detection of DNA biomarkers. [ABSTRACT FROM AUTHOR]

Bismuth bromide (α-Bi4Br4) can demonstrate various exotic topological states, including higher-order topological insulator with hinge states and quantum spin Hall insulator with helical edge states. To date, α-Bi4Br4 nanowires can be obtained by using the exfoliation method from the bulk. However, it is still a great challenge to efficiently prepare α-Bi4Br4 nanowires suitable for potential applications, e.g., saturable absorber in ultrafast pulsed fiber lasers. Here, we report the controllable growth of α-Bi4Br4 thin films consisting of nanowires via molecular beam epitaxy technique. We show that the morphology of the α-Bi4Br4 nanowires depends on the growth temperature and BiBr3 flux. In addition, we also achieve α-Bi4Br4 nanowires on NbSe2 and gold substrates. Furthermore, we performed the saturable absorption property of α-Bi4Br4 thin films with a modulation depth of 21.58% and mode-locking at 1556.4 nm with a pulse width of 375 fs in the pulsed fiber lasers. Those results demonstrate the synthesis of quasi-1D topological material α-Bi4Br4, which is expected to be used for the fundamental research of topological physics and potential applications in optical devices. [ABSTRACT FROM AUTHOR]

• Using electrochemical biosensors for rapid detection of SARS-CoV-2 gene fragments. • Electrode material selection is Bi2Se3 single crystal obtained by mechanical peeling. • The peak current has a linear relationship with the logarithm of DNA concentration. • There is excellent specificity in identifying DNA, RNA, and viruses. • Sensors can clearly distinguish between positive and negative results. In this study, we have designed an electrochemical biosensor based on topological material Bi 2 Se 3 for the sensitive detection of SARS-CoV-2 in the COVID-19 pandemic. Flake-shaped Bi 2 Se 3 was obtained directly from high-quality single crystals using mechanical exfoliation, and the single-stranded DNA was immobilized onto it. Under optimal conditions, the peak current of the differential pulse voltammetry method exhibited a linear relationship with the logarithm of the concentration of target-complementary-stranded DNA, ranging from 1.0 × 10-15 to 1.0 × 10-11 M, with a detection limit of 3.46 × 10-16 M. The topological material Bi 2 Se 3 , with Dirac surface states, enhanced the signal-to-interference plus noise ratio of the electrochemical measurements, thereby improving the sensitivity of the sensor. Furthermore, the electrochemical sensor demonstrated excellent specificity in recognizing RNA. It can detect complementary RNA by amplifying and transcribing the initial DNA template, with an initial DNA template concentration ranging from 1.0 × 10-18 to 1.0 × 10-15 M. Furthermore, the sensor also effectively distinguished negative and positive results by detecting splitting-synthetic SARS-CoV-2 pseudovirus with a concentration of 1 copy/μL input. Our work underscores the immense potential of the electrochemical sensing platform based on the topological material Bi 2 Se 3 in the detection of pathogens during the rapid spread of acute infectious diseases. [ABSTRACT FROM AUTHOR]

Saturable absorption may be induced at critical pumping power by nonlinear optical effects of nanomaterials, thereby making it possible to generate a high-power ultrafast laser. Recently, Bi4Br4 is theoretically predicted to be a member of topological insulators and is expected to be a promising candidate for saturable absorbers (SAs). We show here that Bi4Br4 features a large modulation depth of 42.3%. The Bi4Br4-based SA enables mode-locking operation at the near-infrared range, as demonstrated here by a 1.5 μm fiber laser with a signal-to-noise ratio (SNR) of 90 dB and a pulse duration of 172 fs. Moreover, the robustness of the Bi4Br4-based SA at relatively high power is of particular interest, which can be proved by a laser's stable operation state. The strong optical nonlinearity and robustness provided by Bi4Br4 may arouse a growing upsurge in the innovation of high-power ultrafast photonic devices and further development of photon applications. [ABSTRACT FROM AUTHOR]

In this work, we designed a facile and label-free electrochemical biosensor based on intrinsic topological insulator (TI) Bi 2 Se 3 and peptide for the detection of immune checkpoint molecules. With topological protection, Bi 2 Se 3 could have robust surface states with low electronic noise, which was beneficial for the stable and sensitive electron transport between electrode and electrolyte interface. The peptides are easily synthesized and chemically modified, and have good biocompatibility and bioavailability, which is a suitable candidate as the recognition units for immune checkpoint molecules. Therefore, the peptide/Bi 2 Se 3 was developed as a suitable working electrode for the electrochemical biosensor. The basic performance of the designed peptide/Bi 2 Se 3 biosensor was investigated to determine the Anti-HA Tag Antibody and PD-L1 molecules. The linear detection range was from 3.6 × 10−10 mg mL−1 to 3.6 × 10−5 mg mL−1, and the detection limit was 1.07 × 10−11 mg mL−1. Moreover, the biosensor also displayed good selectivity and stability. [Display omitted] • Sensitive electrochemical biosensors combined with topological materials and peptides. • High-quality and large-scale topological crystal with few defects as electrodes. • Effective recognition units of peptides for the immune checkpoint. • A large detection range, good selectivity and stability with low detection limit of the sensing assay. • Excellent discernment in the complicated serum environment for clinical application. [ABSTRACT FROM AUTHOR]