Guangyu Shen

Improvement of antibody immobilization using hyperbranched polymer and protein A

For the construction of a well-defined antibody surface, protein A was used as a binding material to immobilize antibodies onto gold-derivatized transducers. The traditional method tends to assemble protein A directly onto the gold-derivatized transducers. In this paper, we tried to indirectly bind protein A onto sensors through hyperbranched polymer (HBP) which was synthesized from p-phenylenediamine and trimesic acid. The three-dimensional structure of HBP and the characteristics including orientation control and biocompatibility of protein A led to highly efficient immunoreactions and enhanced detection system performance. With this strategy, cysteamine monolayer was first assembled onto Au electrodes associated with the piezoelectric quartz crystal; secondly, the cysteamine-modified gold electrode was further modified by the activated HBP; thirdly, protein A was immobilized onto the HBP film; and finally, antibodies were immobilized onto the surface of protein A film for detecting the corresponding antigen. The quartz crystal microbalance immunosensor thus fabricated was applied to detect hepatitis B surface antigen in solutions that ranged from 0.71 to 300 μg mL(-1). The detection limit was estimated to be 0.53 μg mL(-1). The immunosensor holds good selectivity, sensitivity, and repeatability.

Electrochemical immunosensor based on Pd-Au nanoparticles supported on functionalized PDDA-MWCNT nanocomposites for aflatoxin B1 detection.

This paper reports a label-free electrochemical immunosensor for the determination of aflatoxin B1 (AFB1), which is based on a gold electrode modified by a biocompatible film of carbon nanotubes/poly(diallyldimethylammoniumchloride)/Pd-Au nanoparticles (CNTs/PDDA/Pd-Au). The nanocomposite was characterized by transmission electron microscopy and the electrochemical behavior of modified electrodes was investigated by cyclic voltammetry. The CNTs/PDDA/Pd-Au nanocomposites film showed good electron transfer ability, which ensured high sensitivity to detect AFB1 in a range from 0.05 to 25 ng mL(-1) with a detection limit of 0.03 ng mL(-1) obtained at 3σ (where σ is the standard deviation of the blank solution, n = 10). The proposed immunosensor provides a simple tool for AFB1 detection. This strategy can be extended to any other antigen detection by using the corresponding antibodies.

One-step immobilization of antibodies for α-1-fetoprotein immunosensor based on dialdehyde cellulose/ionic liquid composite.

A novel immunosensor for α-1-fetoprotein based on dialdehyde cellulose/ionic liquid composite film as a matrix has been developed. Microcrystalline cellulose was activated by sodium metaperiodate to produce dialdehyde cellulose. Antibodies can be immobilized on the electrode by a one-step method through covalent bonding of the aldehyde groups of dialdehyde cellulose with the amino groups of antibodies, in which no additional chemical cross-linking step is required. Moreover, ionic liquid added can improve the conductivity of the sensing interface and, therefore, can enhance the electrochemical signal. In this work, α-1-fetoprotein was detected within the range from 0.1 to 60ngml(-1) with a detection limit of 0.07ngml(-1) (signal/noise=3). The proposed immunosensor had good specificity and reproducibility. It was used to determine real samples with satisfactory results.

Direct immobilization of antibodies on a new polymer film for fabricating an electrochemical impedance immunosensor.

A new polymer bearing aldehyde groups was designed and synthesized by grafting 4-pyridinecarboxaldehyde onto poly(epichlorohydrin). Antibodies can be directly immobilized on the surface of the polymer film through the covalent bonding of aldehyde groups of the film with amino groups of antibodies. In this study, human immunoglobulin G (IgG) was used as a model analyte for the fabrication of an electrochemical impedance immunosensor. Using the proposed immunosensor, IgG in the range from 0.1 to 80 ng ml(-1) was detected with a detection limit of 0.07 ng ml(-1) (signal/noise [S/N]=3). In addition, the electrochemical impedance immunosensor displays good stability and reproducibility.

Development of an electrochemical aptasensor for thrombin based on aptamer/Pd–AuNPs/HRP conjugates

Using Pd–Au nanoparticles functionalized with an aptamer and horseradish peroxidase (Ap/Pd–AuNPs/HRP), we developed a new electrochemical aptasensor for the detection of thrombin. The thiolated single-stranded DNA used as the capture probe was first self-assembled on a gold electrode. Then the Ap/Pd–AuNPs/HRP conjugates were attached to the electrode surface via the hybridization of the capture probe with thrombin aptamer. In the presence of thrombin, Ap/Pd–AuNPs/HRP conjugates dissociated from the electrode surface due to the formation of a tertiary target–aptamer complex, which reduced the amount of HRP and therefore resulted in the decrease of the electrochemical signal. According to this strategy, thrombin was detected within the range from 0.05 to 50 nM with a detection limit of 3 pM based on S/N = 3. The proposed aptasensor had a good specificity, stability and reproducibility.

The development of an electrochemical immunosensor using a thiol aromatic aldehyde and PAMAM-functionalized Fe3O4@Au nanoparticles

In this work, a novel thiol aromatic aldehyde was synthesized. It can be used as a substrate to directly immobilize antibodies on a gold electrode, for which no additional chemical cross-linker is required. It was also applied as a linker to prepare Fe3O4@Au/PAMAM/Ab2-horseradish peroxidase bioconjugates, which introduced multiple enzymes onto a sensing interface owing to the high surface-to-volume ratio of Fe3O4@Au nanoparticles and many functional groups of the poly(amidoamine) dendrimer (PAMAM). The introduced multiple enzymes greatly improved the detection signal. Under optimal conditions, the proposed electrochemical immunosensor exhibited desirable performance for detection of IgG in the range 0.005-50 ng ml(-1) with a detection limit of 3 pg ml(-1) based on a signal-to-noise ratio of 3. It has great potential application in the area of clinical analysis.

A novel label-free electrochemical immunosensor based on aldehyde-terminated ionic liquid

In this paper, aldehyde-terminated ionic liquid was synthesized and used to fabricate a novel label-free electrochemical immunosensor for the determination of hepatitis B surface antigen. This sensor was formed from a gold electrode which was modified with a composite film containing the aldehyde-functionalized ionic liquid incorporated into nafion and anti-hepatitis B surface antigen antibody probes. Aldehyde-functionalized ionic liquid was used not only as a substrate for antibody immobilization, but also as a good material with high electrical conductivity, which greatly simplified the process of sensor fabrication. The proposed sensor exhibited a good performance in a linear range from 0.05 to 15ngmL-1 with a detection limit of 20pgmL-1 (S/N=3) and provided a novel strategy for clinical detection due to satisfying stability, selectivity and reproducibility.

A label-free electrochemical immunosensor based on a new polymer containing aldehyde and ferrocene groups

In this work, a novel and convenient strategy for synthesis of a well-defined polymer containing both aldehyde and ferrocene functional groups by grafting 4-hydroxybenzaldehyde and ferrocenecarboxylhydrazide onto linear poly (vinylbenzyl chloride) was developed. The designed polymer film (polymer CAF) could be used as a new support matrix for fabrication of a label-free electrochemical immunosensor with high sensitivity, good stability and repeatability. With human IgG as an analyte model, the proposed electrochemical immunosensor showed a linear concentration range from 0.1 to 20ngmL-1 with a detection limit of 0.07ngmL-1 (S/N=3). Moreover, interfering proteins including HSA, IgM, and IgE were added into the analyte, the developed immnnosensor can detect human IgG with high specificity.

The fabrication of a piezoelectric immunosensor based on DNA–antibody conjugate layer

In this article, we report a method of antibody immobilization carried out by hybridizing DNA-antibody conjugates on a mixed self-assembled monolayer composed of DNA thiols and mercaptopropionic acid via sequence-specific hybridization. The proposed method was applied to fabricate an immunosensor for detecting human immunoglobulin G (IgG). Under the optimized experimental conditions, a wide linear range from 50.0 to 500 μg/ml was reached with a detection limit of 30.13 μg/ml. The developed immunosensor possesses advantages such as simple fabrication, wide linear range, easy regeneration, and excellent reproducibility.

A versatile matrix of an ionic liquid functionalized with aldehyde and ferrocene groups for label-free electrochemical immunosensors

A novel ionic liquid functionalized with aldehyde and ferrocene groups was successfully synthesized. It was used to develop a label-free electrochemical immunosensor for the detection of human immunoglobulin G by casting this multifunctional ionic liquid entrapped in a Nafion matrix on a gold electrode. This multifunctional material was redox-active because of the introduction of ferrocene on the surface of the electrode through the covalent attachment of ferrocene to the ionic liquid, which avoided the use of other redox species in the electrolyte solution. In the meantime, the covalent attachment also avoided signal decrease resulting from the leakage of ferrocene into solution. In addition, the versatile ionic liquid can be used as a substrate for direct antibody immobilization due to the existence of the aldehyde group, which greatly simplified the process of sensor fabrication. The proposed sensor exhibited a good performance in a linear range from 0.05 to 35 ng mL−1 with a detection limit of 0.03 ng mL−1 based on 3σ and provided a novel strategy for clinical detection due to its satisfactory stability, selectivity and reproducibility.