Au NP Honeycomb-Patterned Films with Controllable Pore Size and Their Surface-Enhanced Raman Scattering

Honeycomb-patterned films (HPFs) of Au nanoparticles (Au NPs) with pore size controlled by varying the quantity of Au NPs or using modified agents of different mercaptans (C₁₄H₂₉SH, C₁₆H₃₃SH, and C₁₈H₃₇SH) were prepared. The strength of the HPFs containing Au NPs can be enhanced because of the addition of polymers including polystyrene, poly­(l-lactic acid), and poly­(methyl methacrylate-<i>co</i>-ethyl acrylate). With an increase in the amount of polymer and the number of Au NPs or the chain length of the modified agents, the pore size of HPFs decreases, indicating that the pore size can be well controlled by adjusting the above factors. Interestingly, HPFs with elliptical pores that were created by the direction of the air flow were observed. The pore diameter on the outer rim is smaller than that in the center, which should be because of the subordinate evaporation of the solvent in the center. Sponge structures were observed in the cross sections of the walls of HPFs, which should be produced by microphase separation. The HPFs consisting of Au NPs with controllable pore size exhibited stronger surface-enhanced Raman scattering. We believe that the HPFs composed of metal NPs such as Au, Ag, and Cu are exploited in multispectral scanners, nanophotons, and sensors

Corallite-like Magnetic Fe₃O₄@MnO₂@Pt Nanocomposites as Multiple Signal Amplifiers for the Detection of Carcinoembryonic Antigen

A nonenzymatic sandwich-type electrochemical immunosensor using corallite-like magnetic Fe₃O₄@MnO₂@Pt nanocomposites was developed for the sensitive detection of carcinoembryonic antigen (CEA). First, aminated graphene (GS-NH₂) sheets were synthesized from graphite oxide using the Hummers’ method, which was used to immobilize the primary antibody via the active amino groups on the GS-NH₂. Second, corallite-like Fe₃O₄@MnO₂@Pt nanoparticles (NPs) were synthesized and characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). They were used as labels to conjugate with a secondary antibody. The multiple amplification of Fe₃O₄@MnO₂@Pt NPs and the promoted electron transfer of GS-NH₂ lead to a broad linear range from 0.5 pg/mL to 20 ng/mL and a low detection limit with 0.16 pg/mL. In addition, the immunosensor performed with good selectivity and acceptable stability and reproducibility as well. The results are satisfactory when the proposed method has been applied to analyze human serum samples. Thus, there would be a promising future in the early diagnosis of cancer to detect CEA and other tumor markers

Photoelectrochemical Sensor with a Z‑Scheme Fe₂O₃/CdS Heterostructure for Sensitive Detection of Mercury Ions

Mercury (Hg2+) is a highly toxic element and can seriously affect human health. This work proposed a photoelectrochemical (PEC) sensor with a Z-scheme Fe2O3/CdS heterostructure and two thymine-rich DNA strands (DNA-1 and Au@DNA-2) for sensitive detection of Hg2+. The light excitation of the Fe2O3/CdS composite accelerated the electron transfer among Fe2O3, CdS, and the electrode to produce a stable photocurrent response. Upon the recognition of Hg2+ to thymine bases (T) in two DNA strands to form a stable T-Hg2+-T biomimetic structure, the photocurrent response increased with the increasing concentration of Hg2+ due to the opening of electronic transmission channels from Au nanoparticles to Fe2O3/CdS nanocomposite. Under the optimal conditions screened by the Box–Behnken experiments, the proposed PEC sensor showed excellent analytical performance for Hg2+ detection with high sensitivity, a detection limit of 0.20 pM at a signal-to-noise ratio of 3, high selectivity, a detectable concentration range of 1 pM–100 nM, and acceptable stability. The good recovery and low relative standard deviation for the analysis of Hg2+ in lake and tap water samples demonstrated the potential application of the designed Z-scheme Fe2O3/CdS heterostructure in the PEC detection of heavy metal ions

A Compatible Sensitivity Enhancement Strategy for Electrochemiluminescence Immunosensors Based on the Biomimetic Melanin-Like Deposition

In this work, a compatible strategy was demonstrated for the enhancement of detection sensitivity of sandwich-type electrochemiluminescence (ECL) immunosensors. The enhanced signal response was based on the combination of biomimetic melanin-like deposition with the effective ECL quenching ability of quinone-rich biopolymers. Gold nanoparticle-loaded horseradish peroxidase (HRP) was used as a catalytic label for the secondary antibodies. The intrinsic catalytic property of HRP toward hydrogen peroxide (H₂O₂) generates reactive oxygen species, which highly promote the autopolymerization of catecholamines. The resulting fast deposition of quinone-rich biopolymers approaching the luminophor-incorporated sensing platform achieves an obvious ECL quenching. A broad-spectrum tumor marker alpha fetoprotein (AFP) was selected as a model analyte to demonstrate the feasibility of the proposed strategy. Under optimal conditions, a very low detection limit of 0.056 pg mL^–1 was obtained. Two orders of magnitude enhancement was achieved in contrast to the signal response without the step of catalytic biopolymer deposition. The combination of compatible HRP labeling with unique melanin-like deposition has potential as a universal strategy in other ECL bioassays

Sulfur-Doped Graphene-Based Immunological Biosensing Platform for Multianalysis of Cancer Biomarkers

The accurate tumor marker detection at an early stage can prevent people from getting cancer to a great extent. Herein, a novel tri-antibody dual-channel biosensing strategy is applied in multianalysis of carcino-embryonic antigen (CEA) and nuclear matrix protein 22 (NMP22). In this immunosensor fabrication process, graphene oxide/polyaniline nanostructures are used as matrix and mesoporous NKF-5-3 is used as labels. Two kinds of antigens can be obtained from the signals of neutral red and toluidine blue, respectively, which are modified on the labels. In this tri-antibody dual-channel biosensing platform, sulfur-doped graphene sheet is synthesized by click chemistry as the framework structure. Majority of the incubations are conducted in individual steps, which ensure the surface incubation more tightly. The detection limit of NMP22 and CEA are 25 and 30 fg/mL, respectively. The low detection limit and excellent stability can ascribe to the tri-antibody dual-channel strategy, which makes the sensor platform from surface to the space. The clinical urine sample analysis achieves a good performance. The urine-based test can avoid the secondary injury on hemophilia or ischemic patients, displaying a potential application in clinical diagnosis

Photoelectrochemical Immunosensor Based on a 1D Fe₂O₃/3D Cd-ZnIn_2.2S_<i>y</i> Heterostructure as a Sensing Platform for Ultrasensitive Detection of Neuron-Specific Enolase

Lung cancer is a high-mortality cancer related to the concentration of neuron-specific enolase (NSE). In this work, a sandwich-type photoelectrochemical (PEC) immunosensor was constructed for ultrasensitive detection of NSE, which is based on iron trioxide/indium zinc cadmium sulfide (Fe2O3/Cd-ZnIn2.2Sy) as a sensing platform and Ag-modified polyaniline (Ag@PANI) as a signal amplification label. The 1D Fe2O3 porous nanorods with a large specific surface area were synthesized by calcination of Fe-MIL-88A and etching of NaOH. To improve the photocurrent response, the 3D architecture Cd-ZnIn2.2Sy was combined with the 1D Fe2O3 porous nanorods to form a 1D Fe2O3/3D Cd-ZnIn2.2Sy heterostructure. Specifically, the Fe2O3/Cd-ZnIn2.2Sy heterostructure with a good energy level matching (the two can form a stepped energy level matching, which accelerates the transfer rate of electrons) can improve the separation efficiency of electron–hole pairs (e–/h+) under visible light irradiation, which enhances the photocurrent response. Ag@PANI has a strong electron transport capability and can be used as a secondary antibody marker for the signal amplification of the immunosensor. The sensor exhibits a good linear detection range of 100 fg/mL to 100 ng/mL with a low detection limit of 33.5 fg/mL. Moreover, the constructed sandwich-type PEC immunosensor shows good performance and possesses excellent specificity, selectivity, and stability over a period of 4 weeks for NSE detection. With these excellent properties, the immunosensor can be extended to analyze and diagnose other disease biomarkers

Electrochemiluminescence Sensor with Controlled-Release Triggering Electrostatic Attraction Elimination Mechanism for Trenbolone Trace Detection

A controlled-release strategy can meet the needs of sensitive environmental monitoring for pollutants through a self-on/off mode. In this work, an electrochemiluminescence (ECL) biosensor with controlled-release triggering electrostatic attraction elimination and biomolecular stimulated response strategies was constructed to detect environmental steroid hormones sensitively. The blocked pores on the aminated mesoporous silica nanocontainers were opened by specific binding between the trenbolone (TB) antigen and the antibody. The released l-cysteine counteracted the negative charge on the MnO2 NF surface through the redox reaction between –SH and MnO2, making the electrostatic interaction between the MnO2 NFs and the Ru­(dcbpy)32+ disappear. Ru­(dcbpy)32+ released an ECL signal on the electrode, thus completing the controlled-release triggering electrostatic attraction elimination strategy. In addition, with the TB antibody as the target and the competition strategy between the TB antigen and the standard substance, the constructed controlled-release ECL biosensor was used to detect the TB standard substance. Moreover, MnO2 NFs as the substrate of the ECL biosensor increased the active specific surface area of the electrode, effectively catalyzing the production of OH• and O2•–, thus endowing the ECL biosensor with coreactant-catalytic enhancement characteristic and further improving its ECL performance. This sensitive signal response brought about a low limit of detection of 2.53 fg/mL for the constructed ECL biosensor, which contributed a feasible idea for efficient trace analysis of pollutants in the environment

Synthesis of Self-Supported Amorphous CoMoO₄ Nanowire Array for Highly Efficient Hydrogen Evolution Reaction

Water electrolysis is known as the most environmental friendly and renewable technology to generate hydrogen. To make it more energy-efficient, development of a promising cathodic hydrogen evolution reaction electrocatalyst is important. In this communication, amorphous CoMoO₄ nanowire array on Ti mesh (CoMoO₄ NWA/Ti) was synthesized via a simple two-step hydrothermal method. As a three-dimensional hydrogen-evolving electrode, CoMoO₄ NWA/Ti shows superior catalytic activity in 1.0 M KOH and demands overpotentials of only 81 and 243 mV to achieve current densities of 10 and 100 mA cm^–2, respectively. Remarkably, it also has long-term electrochemical durability

Deciphering Piperidine Formation in Polyketide-Derived Indolizidines Reveals a Thioester Reduction, Transamination, and Unusual Imine Reduction Process

Piperidine and indolizidine are two basic units of alkaloids that are frequently observed in natural and synthetic compounds. Their biosynthesis in natural products is highly conserved and mostly derived from the incorporation of lysine cyclization products. Through in vitro reconstitution, we herein identified a novel pathway involving a group of polyketide-derived indolizidines, which comprises the processes of tandem two-electron thioester reduction, transamination, and imine reduction to convert acyl carrier protein (ACP)-tethered polyketide chains into the piperidine moieties of their indolizidine scaffolds. The enzymes that catalyze the imine reduction are distinct from previous known imine reductases, which have a fold of acyl-CoA dehydrogenase but do not require flavin for reduction. Our results not only provide a new way for the biosynthesis of the basic units of alkaloids but also show a novel class of imine reductases that may benefit the fields of biocatalysis and biomanufacturing

Nanobody-Based Electrochemical Immunoassay for Ultrasensitive Determination of Apolipoprotein-A1 Using Silver Nanoparticles Loaded Nanohydroxyapatite as Label

Nanobodies (Nbs), derived from camelid heavy-chain antibodies, have distinct advantages over conventional antibodies in immunoassay. In this work, Nbs (Nb11 and Nb19) that can bind to different epitopes on apolipoprotein-A1 (Apo-A1) were screened out from an immunized Bactrian camel for the first time. Nb11 was used as capture antibody and fixed on gold nanoparticles (Au NPs) modified screen-printed carbon electrode (SPCE). The silver nanoparticles loaded nanohydroxyapatite (Ag-nHAP) was used as signal tag to label secondary antibody Nb19. A sandwich-type immunological reaction occurred between Apo-A1 and the two Nbs, which brought the Ag-nHAP to the SPCE surface. After the Ag-nHAP were acidically dissolved in the microelectrolytic cell of the SPCE, stripping voltammetric measurement for the released silver ions was performed to obtain an amplified signal. The peak current values increased by the logarithmic values of Apo-A1 concentrations from 10^–4 to 50 ng mL^–1 under optimal conditions. The detection limit was calculated to be 0.02 pg mL^–1. This method was used for the serum samples analysis and achieved satisfactory results. The low cost and high sensitivity make the electrochemical immunosensor suitable for the Apo-A1 detection, which may find promising application in other fields