Huayu Yi

A sensitive electrochemical aptasensor based on palladium nanoparticles decorated graphene–molybdenum disulfide flower-like nanocomposites and enzymatic signal amplification

In the present study, with the aggregated advantages of graphene and molybdenum disulfide (MoS2), we prepared poly(diallyldimethylammonium chloride)-graphene/molybdenum disulfide (PDDA-G-MoS2) nanocomposites with flower-like structure, large surface area and excellent conductivity. Furthermore, an advanced sandwich-type electrochemical assay for sensitive detection of thrombin (TB) was fabricated using palladium nanoparticles decorated PDDA-G-MoS2 (PdNPs/PDDA-G-MoS2) as nanocarriers, which were functionalized by hemin/G-quadruplex, glucose oxidase (GOD), and toluidine blue (Tb) as redox probes. The signal amplification strategy was achieved as follows: Firstly, the immobilized GOD could effectively catalyze the oxidation of glucose to gluconolactone, coupling with the reduction of the dissolved oxygen to H2O2. Then, both PdNPs and hemin/G-quadruplex acting as hydrogen peroxide (HRP)-mimicking enzyme could further catalyze the reduction of H2O2, resulting in significant electrochemical signal amplification. So the proposed aptasensor showed high sensitivity with a wide dynamic linear range of 0.0001 to 40 nM and a relatively low detection limit of 0.062 pM for TB determination. The strategy showed huge potential of application in protein detection and disease diagnosis.

An electrochemical aptasensor for thrombin using synergetic catalysis of enzyme and porous Au@Pd core–shell nanostructures for signal amplification

In this work, a sensitive electrochemical aptasensor for thrombin (TB) based on synergetic catalysis of enzyme and porous Au@Pd core-shell nanostructure has been constructed. With the advantages of large surface area and outstanding catalytic performance, porous Au@Pd core-shell nanostructures were firstly employed as the nanocarrier for the immobilization of electroactive toluidine blue (Tb), hemin/G-quadruplex formed by intercalating hemin into the TB aptamer (TBA) and glucose oxidase (GOx). As a certain amount of glucose was added into the detection cell, GOx rapidly catalyzed the oxidation of glucose, coupling with the local generation of H2O2 in the presence of dissolved O2. Then, porous Au@Pd nanoparticles and hemin/G-quadruplex as the peroxidase mimics efficiently catalyzed the reduction of H2O2, amplifying the electrochemical signal and improving the sensitivity. Finally, a detection limit of 0.037pM for TB was achieved. The excellent performance of the aptasensor indicated its promising prospect as a valuable tool in simple and cost-effective TB detection in clinical application.

Ultrasensitive thrombin detection based on direct electrochemistry of highly loaded hemoglobin spheres-encapsulated platinum nanoparticles as labels and electrocatalysts.

For the first time, a sandwich-type electrochemical method was proposed for ultrasensitive thrombin (TB) detection based on direct electrochemistry of highly loaded hemoglobin spheres-encapsulated platinum nanoparticles (PtNPs@Hb) as labels and electrocatalysts. The prepared PtNPs@Hb not only exhibited good biocompatibility, excellent electrocatalytic activity, but also presented redox activity of Hb. Thus, it was employed for the fabrication of aptasensor without any extraneous redox mediators, leading to a simple preparation process for the aptasensor. The high loading of Hb spheres as redox mediators could enhance the electrochemical signal. Importantly, the synergetic electrocatalytic behavior of Hb and PtNPs toward H2O2 reduction greatly amplified the electrochemical signal, resulting in the high sensitivity of aptasensor. Consequently, under optimal conditions, the designed aptasensor exhibited a lower detection limit of 0.05 pM and wide dynamic linear range from 0.15 pM to 40 nM for TB detection. Additionally, the proposed mediator-free and signal-amplified electrochemical aptasensor showed great potential in portable and cost-effective TB sensing devices.

A ‘signal on-off’ electrochemical peptide biosensor for matrix metalloproteinase 2 based on target induced cleavage of a peptide

In this work, a ‘signal on-off’ electrochemical peptide biosensor was developed for the determination of matrix metalloproteinase 2 (MMP-2) on the basis of target induced cleavage of a specific peptide. The prepared single-stranded DNA–porous platinum nanoparticles–peptide (S1–pPtNPs–P1) bioconjugates were employed as nanoprobes, where the specific peptide (P1, biotin–Gly–Pro–Leu–Gly–Val–Arg–Gly–Lys–Gly–Gly–Cys) was used as a cleavage-sensing element, offering the capability of ‘on-off’ electrochemical signalling for the target MMP-2. As for the construction of the biosensor, S1–pPtNPs–P1 was immobilized on the electrode surface through the conjunction of biotin–streptavidin. Then, hybridization chain reaction (HCR) was triggered to embed the electroactive thionine (Thi). The pPtNPs could effectively catalyze the decomposition of added H2O2, resulting in the electrochemical signal of Thi being enhanced significantly (‘signal on’ state). Upon sensing cleavage with MMP-2, pPtNPs and eletroactive Thi left the electrode surface, leading to an observable decrease in the electrochemical signal of Thi (‘signal off’ state). Compared with other methods of detecting MMP-2, the proposed ‘signal on-off’ electrochemical peptide biosensor exhibited an improved sensitivity with a detection limit of 0.32 pg mL−1 and wide linear range from 1 pg mL−1 to 10 ng mL−1.

Dendritic Pt@Au nanowires as nanocarriers and signal enhancers for sensitive electrochemical detection of carcinoembryonic antigen

Highly sensitive detection of carcinoembryonic antigen (CEA) is very important in clinical diagnosis and treatment assessment of cancers. In this work, we proposed a sensitive and selective electrochemical aptasensor for CEA detection using dendritic Pt@Au nanowires (Pt@AuNWs) as nanocarriers and electrocatalysts. With many advantages such as large specific surface area, good conductivity, excellent electrocatalytic activity and high stability, dendritic Pt@AuNWs were first employed as nanocarriers for immobilizing abundant thiol-terminated CEA aptamer 2 (CEAapt2) and redox-active toluidine blue (Tb), resulting in the formation of AuNWs–CEAapt2–Tb bioconjugate. In the presence of CEA, the proposed bioconjugate was captured onto the electrode surface through “sandwich” tactics. The electrochemical response was then triggered and further enhanced due to the favorable catalysis capacity of dendritic Pt@AuNWs with peroxidase mimic activity for the reduction of H2O2 added into the electrolytic cell, from which an improved sensitivity benefited and was successfully achieved. Under the optimal experimental conditions, the proposed aptasensor exhibited a linear response to CEA in the range of 0.001 ng mL−1 to 80 ng mL−1 and the limit of detection (LOD) is 0.31 pg mL−1. Moreover, the aptasensor exhibited good selectivity, stability and reproducibility, which indicated its potential applications in clinical diagnostics.