Sandwich-type electrochemical aptasensor for sensitive detection of myoglobin based on Pt@CuCo-oxide nanoparticles as a signal marker.

When an acute myocardial infarction (AMI) occurs, myoglobin (Mb) is the biomarker whose concentration firstly increases, and the high sensitive detection of Mb is critical for early diagnosis of AMI. Herein, a sandwich-type electrochemical aptasensor for the sensitive detection of Mb was constructed by using Pt@Cu1.33OCo0.83O as the signal marker. On one hand, nano-flower-like Cu1.33OCo0.83O was synthesized by hydrothermal method and Pt nanoparticles (Pt NPs) were loaded on its surface. Pt@Cu1.33OCo0.83O could immobilize aptamer 2 (Apt2) successfully by the Pt-S bond. And because of the synergistic effect between Pt and bimetallic oxide, Pt@Cu1.33OCo0.83O had an excellent catalytic effect on the signal source of hydrogen peroxide (H2O2) to amplify the current signal, which enhance the sensitivity of the aptasensor. On the other hand, the screen-printed gold electrode (SPGE) was used as the sensing base, which had good conductivity and ensured the immobilization of aptamer 1 (Apt1). The quantitative detection of Mb was achieved by specific recognition between Mb and Apt1, Apt2. As a result, the constructed electrochemical aptasensor had a good linear range (1-1500 ng/mL) with a low detection limit (LOD) of 0.128 ng/mL (S/N = 3), and a high sensitivity of 29.47 µA dec-1. The aptasensor also realized the detection of Mb in human serum samples with good accuracy, and the results were consistent with the hospital's biochemical indicators, which demonstrated the potential application of the prepared sensor in the clinical detection of Mb.

An electrochemical aptasensor based on multi-walled carbon nanotubes loaded with PtCu nanoparticles as signal label for ultrasensitive detection of adenosine.

Adenosine, as an endogenous nucleoside modulator, plays an important role in heart rate regulation, neurotransmission, and control of the respiratory system and thus it is significantly important to realize its sensitive detection. Herein, a highly sensitive electrochemical aptasensor for adenosine detection was proposed by using multi-walled carbon nanotubes (MWCNTs) as support matrix loading PtCu nanoparticles (PtCu-MWCNTs) to amplify signal. On one hand, disposable screen-printing gold electrodes (SPGEs) were used as superb sensing base to ensure the stable connection of aptamers 1 (ssDNA1). On the other hand, the PtCu-MWCNTs complex was synthesized through a one-pot method, which not only can precisely control the proportion of metal mass in the product but also exhibited superior electrocatalytic activity towards H2O2. The recognition reactions were achieved by stepwise incubation of ssDNA1, ssDNA2-PtCu-MWCNTs (denoted as ssDNA2-label), and adenosine on the SPGEs. As a result, the constructed electrochemical aptasensor exhibited a wide linear range from 10 nM to 1.0 µM with a low detection limit of 1.0 nM (S/N = 3) for adenosine detection. The aptasensor also successfully realized the adenosine detection in human serum samples, which means that the proposed aptasensor holds a potential application in point-of-care detection.

Flexible electrochemical sensor with Fe/Co bimetallic oxides for sensitive analysis of glucose in human tears.

The construction of uniformly dispersed structure with abundant active sites is crucial for fast electron transport and advancing electrocatalytic reactions. Herein, FexCoyO4-rGO was prepared by depositing Fe and Co bimetallic oxides in-situ on reduced graphene oxide through a simple process combined hydrothermal reaction and calcination. Fe was elaborately introduced into the synthesis of metal oxides to alleviate the aggregation of cobalt oxides and obtain nanocomposites with homogeneously structured and abundant redox sites, and the bimetallic oxides nanomaterials had enhanced electrocatalysis under the synergistic effect. The flexible electrode prepared from FexCoyO4-rGO exhibited excellent detection performance for glucose with a detection limit down low to 0.07 µM and a sensitivity of 1510 µM cm-2 mA-1. The adoption of flexible substrates improved the wearability of the electrode and broadened its practicality for detecting biomarkers on the skin surface. The constructed sensor was successfully used in the dynamic analysis of glucose content in tears, and the results were highly consistent with the test outcome of a commercial test kit, demonstrating its application prospects in non-invasive epidermal diabetes mellitus diagnosis.

Sandwich-type electrochemical aptasensor based on Au-modified conductive octahedral carbon architecture and snowflake-like PtCuNi for the sensitive detection of cardiac troponin I.

The cardiac troponin I (cTnI) detection is increasingly significant given its promising value in the clinical acute myocardial infarction diagnosis. Here a sensitive sandwich-type cTnI electrochemical aptasensor was developed by using zirconium-carbon loaded with Au (Au/Zr-C) as electrode-modified material and snowflake-like PtCuNi catalyst as label material. The Au/Zr-C was prepared from a carbonation process and a reduction step. The PtCuNi was synthesized by a one-pot hydrothermal reaction. On the one hand, due to its many merits of large effective area, rich pores, high degree of graphitization, the assistance of Au, the Au/Zr-C exhibited remarkable electronic conductivity but low catalytical capacity, thus improving the electrochemical property but lowing the background signal of electrode. On the other hand, because of its accessible active sites of the special snowflake-like structure and the synergy of three elements, the PtCuNi catalyst presented excellent catalytic activity and improved stability compared to binary alloy. The recognition reactions were achieved by stepwise incubation of aptamer 1, cTnI, and aptamer 2-PtCuNi (denoted as Apt2-label) on the Au/Zr-C-modified electrode. The electrocatalytic signals of the immobilized Apt2-label towards the H2O2 reduction were recorded in all tests for cTnI analysis. Consequently, this cTnI aptasensor exhibited excellent performance involving a wide linear range of 100 ng mL-1 to 0.01 pg mL-1 with a detection limit of 1.24 × 10-3 pg mL-1 (S/N = 3), good selectivity, satisfying reproducibility, outstanding stability, and good recovery.

Two-dimensional mesoporous nitrogen-rich carbon nanosheets loaded with CeO2 nanoclusters as nanozymes for the electrochemical detection of superoxide anions in HepG2 cells.

Two-dimensional (2D) porous carbon-based composite nanosheets loaded with metal oxide nanoclusters are expected to be promising electrocatalysts for high-performance electrochemical sensors. However, for this complicated composite material, strict reaction conditions and complex synthesis steps limit its general application in electrochemical detection. Here we present a facile method to fabricate 2D mesoporous nitrogen-rich carbon nanosheets loaded with CeO2 nanoclusters (2D-mNC@CeO2), for fabricating superoxide anions (O2•-) electrochemical sensor. The method is based on block copolymers self-assembly and the affinity of polydopamine to metal ions to obtain organic-inorganic hybrid, which can be directly converted into 2D-mNC@CeO2 through carbonization strategy without structural deterioration. Characterizations demonstrate that the 2D-mNC@CeO2 owned the 2D N-doped carbon structure with an interlinked hierarchical mesoporous and the uniformly dispersed CeO2 nanoclusters on the surface. Benefitted from the unique structure, the 2D-mNC@CeO2 shortens electron transfer distance, enhances mass transfer efficiency, exposes numerous active sites, and obtain a high Ce3+/Ce4+ ratio for improving electrocatalytic performance. The 2D-mNC@CeO2/SPCEs sensors for O2•- detection has a detection limit of 0.179 µM (S/N = 3) and sensitivity of 401.4 µA cm-2 mM-1. The sensors can be applied to capture electrochemical signals of O2•- released from HepG2 cells, demonstrating the application potential of the sensors to monitor O2•- in biological fields.

Sandwich-type electrochemical aptasensor based on hollow mesoporous carbon spheres loaded with porous dendritic Pd@Pt nanoparticles as signal amplifier for ultrasensitive detection of cardiac troponin I.

Signal amplification is crucial to improve the sensitivity for the electrochemical detection of cardiac troponin I (cTnI), one of the ideal biomarkers for early acute myocardial infarction (AMI) diagnosis. Herein, we developed a novel signal amplification strategy to construct a sandwich-type electrochemical aptasensor for the detection of cTnI. Core-shell Pd@Pt dendritic bimetallic nanoparticles loaded on melamine modified hollow mesoporous carbon spheres (Pd@Pt DNs/NH2-HMCS) was prepared as labels to conjugate with thiol-modification DNA aptamers probe for signal amplification. While introducing numerous amino groups, the melamine functionalized hollow mesoporous carbon spheres (NH2-HMCS) retained the edge-plane-like defective sites for the adhesion and electrocatalytic reduction of H2O2. With the unique characteristics of NH2-HMCS, it not only enhanced the dispersity and loading capacity of core-shell Pd@Pt dendritic bimetallic nanoparticles (Pd@Pt DNs), but also improved the stability of bonding by the affinity interaction between Pd@Pt DNs and amino groups of melamine. Meanwhile, the synergistic catalysis effect between Pd@Pt DNs and NH2-HMCS significantly enhanced the electrocatalytic reduction of H2O2 and further amplified the signal. Under optimal conditions, this recommended aptasensor for cTnI detection displayed a wide dynamic range from 0.1 pg/mL to 100.0 ng/mL and a low detection limit of 15.4 fg/mL (S/N = 3). The sensor also successfully realized the analysis of cTnI-spiked human serum samples, meaning potential applications in AMI diagnosis.

A novel signal amplification label based on AuPt alloy nanoparticles supported by high-active carbon for the electrochemical detection of circulating tumor DNA.

The detection of circulating tumor DNA (ctDNA) has increasingly received a great deal of attention considering its significance in cancer diagnosis. And the signal amplification plays an important role in the development of sensitive ctDNA biosensors. Herein, the nanocomposites (denoted as HAC-AuPt), integrating from high-active carbon (HAC) and AuPt alloy nanoparticles, were synthesized and subsequently used as a signal amplification label to fabricate a sandwich-type ctDNA electrochemical biosensor. Characterizations demonstrated that HAC presents uniform size distribution and AuPt alloy nanoparticles were successfully loaded on HAC. The current response could be amplified to a great extent by the resultant HAC-AuPt due to its excellent electrochemical property. The nanocomposites were further bounded with DNA signal probes (SPs) via Au-S or Pt-S assembly to form SPs-label. After the capture probes (CPs) were immobilized on the electrode surface, the target DNA (tDNA) and SPs-label were stepwise incubated on the CPs-modified electrode, thus forming a sandwich-type structure. By monitoring the catalytic signal of HAC-AuPt towards the reduction process of H2O2, this biosensor provided a wide linear range of 10-8 mol/L - 10-16 mol/L with a low detection limit of 3.6 × 10-17 mol/L (S/N = 3) for the detection of the tDNA. Furthermore, obvious differences in response signals among different DNAs were observed benefitting from the excellent selectivity of the biosensor. Besides, the long-term stability, reproducibility, and recovery rate were proved to be outstanding. These results indicate that the established biosensor holds a potential application in the clinical diagnosis of ctDNA.

Facile synthesis of ultrathin two-dimensional graphene-like CeO2-TiO2 mesoporous nanosheet loaded with Ag nanoparticles for non-enzymatic electrochemical detection of superoxide anions in HepG2 cells.

Here we presented a new facile strategy to fabricate ultrathin two-dimensional (2D) metal oxide nanosheets, by using polydopamine-coated graphene (rGO@PDA) as a template under simply wet-chemical conditions. Based on the strategy, graphene-like CeO2-TiO2 mesoporous nanosheet (MNS-CeO2-TiO2) was prepared and was loaded with dispersive Ag nanoparticles (AgNPs) to obtain effective electrocatalysts (denoted as Ag/MNS-CeO2-TiO2) for electrochemical detection of superoxide anion (O2•-). Characterizations demonstrated that MNS-CeO2-TiO2 exhibited ultrathin thickness, larger specific surface area, and pore volume in comparison with its bulk counterpart. The above properties of MNS-CeO2-TiO2 shorten electron transmission distance, promotes mass transfer, and is conducive to the dispersion of post-modified AgNPs. Therefore, the recommended Ag/MNS-CeO2-TiO2 sensors (denoted as Ag/MNS-CeO2-TiO2/SPCE) exhibited satisfactory properties, including the sensitivity of 737.1 µA cm-2 mM-1, the detection limit of 0.0879 µM (S/N = 3), and good selectivity. Meanwhile, the sensors also successfully realized in the online monitoring of O2•- released from HepG2 cells, meaning the prepared sensors had practical application potential towards the analysis of O2•- in biological samples.

Carbon-mediated synthesis of shape-controllable manganese phosphate as nanozymes for modulation of superoxide anions in HeLa cells.

Transition metal phosphates have shown great potential as nanozymes for selective detection of reactive oxygen species (ROS), but its application has been hindered by the complicated synthesis and difficulty in shape and size control. Herein, we present a facile method to fabricate transition metal phosphates by using hollow carbon structures as substrates. Manganese phosphate is a typical Nanozyme used in this design and the shape and size of the Mnx(PO4)y layer can be efficiently controlled by altering the carbon substrates. Characterization demonstrated that Mnx(PO4)y layer modified hollow carbon sphere (Mn-MPSA-HCS) and hollow carbon cubic (Mn-MPSA-HCC) were successfully prepared and used as nanozymes for superoxide detection. The established electrochemical sensor was employed in the online monitoring of drug stimulated superoxide anions released from cancer cells. This method can be adapted as a general way to prepare transition metal phosphate layers with various controllable shapes and sizes as nanozymes for different uses in the future.

Fabricating carbon-nanotubes-based porous foam for superoxide electrochemical sensing through one-step hydrothermal process induced by phytic acid.

The detection of superoxide anions (O2•-) is widely considered as a potential way for cancer diagnosis and the development of enzyme-mimic catalysts is the main challenge in the establishment of electrochemical sensors for O2•- sensing in real samples. Here we present a novel enzyme- and metal-free electrochemical catalyst for superoxide (O2•-) sensing based on the widely-used carbon nanotubes (CNT). Through a one-step hydrothermal process induced by phytic acid (PA), CNT-based porous foam (PACNTF) was successfully obtained. Characterizations demonstrated the enhanced defect and disorder degree of PACNTF after PA treatment, which leaded to the increased active sites of PACNTF for electron transfer and the adhesion of O2•- during the electrochemical process. As a result, the PACNTF presented higher conductivity and larger current response toward O2•- sensing when compared with CNT precursor and CNTF without PA treatment. The sensitivity of PACNTF/SPCE was calculated to be 1230 µA cm-2 mM-1 in the linear range of 0-193.6 µM (R2 = 0.965) and 373 µA cm-2 mM-1 in the linear range of 193.6-1153.6 µM (R2 = 0.995) with a limit of detection of 0.16 µM (S/N = 3). Further, the PACNTF/SPCE presented fast response toward cell-released O2•- stimulated by Zymosan A. The above results indicated that the fabricated sensor holds potential usage in biological samples.