Jiyang Liu

Three-dimensional electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on monolithic and macroporous graphene foam.

A high performance three-dimensional (3D) electrochemical immunosensor was developed for sensitive detection of the tumor biomarker, carcinoembryonic antigen (CEA). Monolithic and macroporous graphene foam grown by chemical vapor deposition (CVD) served as the scaffold of the free-standing 3D electrode. Immuno-recognition interface was fabricated via simple and non-covalent immobilization of antibody using lectin-mediated strategy. Briefly, the well-known lectin macromolecule (concanavalin A, Con A) monolayer was functionalized on 3D graphene (3D-G) using in-situ polymerized polydopamine as the linker. Then the widely used horseradish peroxidase (HRP)-labeled antibody (anti-CEA) in immunoassays was efficiently immobilized to demonstrate the recognition interface via the biospecific affinity of lectin with sugarprotein. The 3D immunosensor is able to detect CEA with a wide linear range (0.1-750.0ngml(-1)), low detection limit (~90pgml(-1) at a signal-to-noise ratio of 3), and short incubation time (30min). Furthermore, this biosensor was used for the detection of the CEA level in real serum samples.

Highly sensitive and selective detection of cancer cell with a label-free electrochemical cytosensor

Electrochemical methods have attracted considerable attention for developing cytosensing system since they can decrease the cost and time requirement for cell detection with simple instrumentation. Herein, a label-free electrochemical cytosensor with surface-confined ferrocene as signal indicator was developed for highly sensitive and selective detection of cancer cell. With layer-by-layer (LBL) self-assembly technique, positively charged poly(ethylene imine) functionalized with ferrocene (Fc-PEI) and negatively charged single-wall carbon nanotubes (SWNTs) were alternately assembled on 3-mercaptopropionic acid (MPA) modified gold substrate. Folic acid (FA) was covalently bonded onto SWNTs surface to specifically recognize cancer cells according to the high affinity of FA for folate receptor (FR) on cellular surface. The developed cytosensor presented high sensitivity and selectivity for the detection of human cervical carcinoma (HeLa) cell. By using fast-response differential pulse voltammetry (DPV) method, a wide detection range from 10 to 10(6) cells/mL with a detection limit as low as 10 cells/mL was reached even in the presence of a large amount of non-cancerous cells.

G-quadruplex-based ultrasensitive and selective detection of histidine and cysteine

Histidine and cysteine detection is critically important since an abnormal level of histidine or cysteine is an indicator for many diseases. In this paper, we demonstrated a novel label-free, G-quadruplex-based approach for simultaneous detection of histidine and cysteine. The present assay is based on the highly specific interaction among amino acids (histidine or cysteine), Cu(2+) and NMM/G-4 (NMM: N-methylmesoporphyrin IX; G-4: G-quadruplex). The fluorescence intensity of NMM was dramatically enhanced in the presence of G-quadruplex formed from 24GT, which can be effectively quenched by cupric ion (Cu(2+)) due to the chelation of Cu(2+) by NMM as well as the unfolding of G-quadruplex by Cu(2+). The presence of histidine or cysteine will disturb the interaction between Cu(2+) and NMM/G-4 because of the strong binding affinity of Cu(2+) to the imidazole group of histidine or the interaction of Cu(2+) with thiol group in cysteine, leading to distinct fluorescence emission intensity. High selectivity is conferred by the use of cysteine-masking agent N-ethylmaleimide (NEM), which helps to discriminate histidine from cysteine. At last, a novel and simple approach was developed to determine each precise concentration of histidine and cysteine according to the different response of the system with and without NEM. Importantly, histidine can be also detected even in the presence of a large amount of other amino acids. A detection limit as low as 3 nM for histidine and 5 nM for cysteine was obtained by practical measurement rather than conventional calculation (S/N=3), confirming the high sensitivity of the present approach. Meanwhile, this sensing protocol can determine histidine and cysteine in diluted biological samples such as urine, exhibiting great potential to meet the need of practical application.

Functionalization of monolithic and porous three-dimensional graphene by one-step chitosan electrodeposition for enzymatic biosensor.

Biological modification of monolithic and porous 3D graphene is of great significance for extending its application in fabricating highly sensitive biosensors. The present work reports on the first biofunctionalization of monolithic and freestanding 3D graphene foam for one-step preparation of reagentless enzymatic biosensors by controllable chitosan (CS) electrodeposition technology. Using a homogeneous three-component electrodeposition solution containing a ferrocene (Fc) grafted CS hybrid (Fc-CS), glucose oxidase (GOD), and single-walled carbon nanotubes (SWNTs), a homogeneous biocomposite film of Fc-CS/SWNTs/GOD was immobilized on the surface of 3D graphene foam by one-step electrodeposition. The Fc groups grafted on chitosan can be stably immobilized on the 3D graphene surface and keep their original electrochemical activity. The SWNTs doped into the Fc-CS matrix act as a nanowire to facilitate electron transfer and improve the conductivity of the biocomposite film. Combined with the extraordinary properties of 3D graphene foam including large active surface area, high conductivity, and fast mass transport dynamics, the 3D graphene based enzymatic biosensor achieved a large linear range (5.0 μM to 19.8 mM), a low detection limit (1.2 μM), and rapid response (reaching the 95% steady-state response within 8 s) for reagentless detection of glucose in the phosphate buffer solution.

Synthesis of phospholipid monolayer membrane functionalized graphene for drug delivery

In this contribution, lipid monolayer membrane functionalized graphene sheets were prepared using a facile method. Interactions between the graphene and different types of liposomes, including charged and neutral, were also investigated. We found that the anionic liposomes could spontaneously self-organize into lipid monolayer membranes, partially covering the surface of graphene sheets. The resultant lipid monolayer functionalized graphene nanomaterials exhibited high stability in aqueous solution and an excellent performance as carrier for loading the anticancer drug, doxorubicin (DOX), with a high loading capacity of 70%. The loaded drug can be released under pH control. 10% and 14% of the bound DOX was released after 54 h at pH 10.0 and 7.0, respectively. Whereas, about 70% of DOX was released after 54 h at pH 5.0.

A DNA-Based and Electrochemically Transduced Keypad Lock System with Reset Function

Try your lock: A resettable DNA-based keypad lock system with electrochemical current as output signal has been successfully developed as proof of concept (see scheme). The system is triggered to ON only when the inputs are adopted with an appropriate combination and exact sequence. The reset function can be facilely realized.

Label-free electrochemical aptasensor constructed by layer-by-layer technology for sensitive and selective detection of cancer cells

Here, a cytosensor was constructed with ferrocene-appended poly(allylamine hydrochloride) (Fc-PAH) functionalized graphene (Fc-PAH-G), poly(sodium-p-styrenesulfonate) (PSS) and aptamer (AS1411) by layer-by-layer assembly technology. The hybrid nanocomposite Fc-PAH-G not only brings probes on the electrode and also promotes electron transfer between the probes and the substrate electrode. Meanwhile, LBL technology provides more effective probes to enhance amplified signal for improving the sensitivity of the detection. While AS1411 forming G-quardruplex structure and binding cancer cells, the current response of the sensing electrode decreased due to the insulating properties of cellular membrane. Differential pulse voltammetry (DPV) was performed to investigate the electrochemical detection of HeLa cells attributing to its sensitivity of the current signal change. The as-prepared aptasensor showed a high sensitivity and good stability, a widely detection range from 10 to 10(6) cells/mL with a detection limit as low as 10 cells/mL for the detection of cancer cells.

Electrochemical current rectifier as a highly sensitive and selective cytosensor for cancer cell detection

Signal amplification originating from electrochemical current rectifier (ECR) was firstly applied to construct a cytosensor for rapid and non-invasive detection of folate receptor-rich cancer cells with high sensitivity. It exhibits a broad linear range with a detection limit as low as 10 cells mL(-1) even in the presence of a large number of normal cells.

Enzyme immobilization and direct electrochemistry based on a new matrix of phospholipid-monolayer-functionalized graphene.

A new nanocomposite material for enzyme immobilization and subsequent direct electrochemistry and electrocatalysis was developed by using 1,2-dimyristoyl-sn-glycero-3-phospho-(1-rac-glycerol)-phospholipid-monolayer-membrane-modified graphene (DMPG-G). Microperoxidase-11 (MP11) was chosen as a model enzyme to investigate the composite system. Owing to the improved conductivity and biocompatible microenvironment, MP11 that was immobilized in the matrix of the DMPG-G nanocomposite (DMPG-G-MP11) effectively retained its native structure and bioactivity. DMPG-G-MP11-modified glassy carbon electrode (DMPG-G-MP11/GCE) exhibited a pair of well-defined quasi-reversible redox peaks of MP11 and showed high electrocatalytic activity towards hydrogen peroxide (H(2)O(2)). The linear response of the developed biosensor for the determination of H(2)O(2) ranged from 2.0×10(-6) to 4.5×10(-4)  M with a detection limit of 7.2×10(-7)  M. This biosensor exhibited high reproducibility and long-term storage stability. The promising features of this biosensor indicate that these lipid-graphene nanocomposites are ideal candidate materials for the direct electrochemistry of redox proteins and that they could serve as a versatile platform for the construction of a third-generation biosensor.

Multiple pH-responsive graphene composites by non-covalent modification with chitosan

Multiple pH-sensitive composites have been prepared through non-covalently functionalizing chemically converted graphene (CCG) with chitosan. Chtiosan exhibits as polybases and CCG shows characteristics of polyacids. Owing to the synergistic effects of chitosan and CCG, chitosan decorated graphene (CS-G) presents a multiple pH-responsive behavior that it can be dispersed well whether in acidic or in basic solution but aggregated in near-neutral solution. After CS-G was modified through a controlled deposition and cross-linking process of chitosan, the resultant cross-linked chitosan decorated graphene (CLCS-G) can be converted to a different pH-sensitive material that disperses only in acidic solution. Both CS-G and CLCS-G present a reversible switching between dispersed and aggregated states with pH as a stimulus. The unique pH response mechanisms of CS-G and CLCS-G have been further investigated by zeta potential analysis. Based on the unique pH-responsive property of CS-G, a stable and repeatable pH-driven switch was developed for monitoring pH change.