Amperometric micro-immunosensor for the detection of tumor biomarker

Biosensors in clinical chemistry - 2011 update

Research activity and applications of biosensors for measurement of analytes of clinical interest over the last eight years are reviewed. Nanotechnology has been applied to improve performance of biosensors using electrochemical, optical, mechanical and physical modes of transduction, and to allow arrays of biosensors to be constructed for parallel sensing. Biosensors have been proposed for measurement of cancer biomarkers, cardiac biomarkers as well as biomarkers for autoimmune disease, infectious disease and for DNA analysis. Novel applications of biosensors include measurements in alternate sample types, such as saliva. Biosensors based on immobilized whole cells have found new applications, for example to detect the presence of cancer and to monitor the response of cancer cells to chemotherapeutic agents. The number of research reports describing new biosensors for analytes of clinical interest continues to increase; however, movement of biosensors from the research laboratory to the clinical laboratory has been slow. The greatest impact of biosensors will be felt at point-of-care testing locations without laboratory support. Integration of biosensors into reliable, easy-to-use and rugged instrumentation will be required to assure success of biosensor-based systems at the point-of-care.

A folding-based electrochemical aptasensor for detection of vascular endothelial growth factor in human whole blood

We herein report a folding-based electrochemical DNA aptasensor for the detection of vascular endothelial growth factor (VEGF) directly in complex biological samples, including blood serum and whole blood. The electrochemical signal generation is coupled to a large, target-induced conformational change in a methylene blue-modified and surface immobilized anti-VEGF aptamer. The sensor is sensitive, selective and essentially reagentless: we can readily detect VEGF down to 5 pM (190 pg/mL) directly in 50% blood serum. Similar to other aptasensors of this class, the VEGF sensor is also regenerable and reusable. In addition, the sensor performs comparably well even when fabricated on a gold-plated screen-printed carbon electrode and can potentially be implemented as a cost-effective, single-use biosensor for diseases diagnosis and therapy monitoring. The exceptional sensitivity, selectivity, and reusability of this electrochemical aptasensor platform suggest it may be a promising strategy for a wide variety of sensing applications.

Assessment of oxidative DNA damage and repair at single cellular level via real-time monitoring of 8-OHdG biomarker

8-Hydroxydeoxyguanosine (8-OHdG) is the most important and best-documented biomarker of oxidative stress, which is involved in the instigation of various diseases. 8-OHdG levels correlate to oxidative DNA damage which is known to be the root cause of a variety of age-related chronic diseases. The purpose of our research was to develop a detection strategy capable of measuring 8-OHdG in real-time at the surface of a single cell. Activated carbon fiber microelectrodes were used as the sensing platform. The microelectrodes were used to measure 8-OHdG release from single lung epithelial cells under the influence of nicotine. In order to evaluate the direct role of nicotine in tobacco induced genotoxicity, we studied the influence of parameters such as nicotine concentration and exposure times on 8-OHdG secretion. 2-8 mM nicotine solutions induced dose-dependent DNA damage in single cells, which was observed via amperometric measurements of secreted 8-OHdG biomarker. Real-time 8-OHdG measurements from single cells exposed to 4 mM nicotine solution revealed cessation of 8-OHdG secretion after 110 min. We have successfully outlined a methodology to detect 8-OHdG at the surface of single cells. A similar protocol can be used to evaluate oxidative DNA damage and repair mechanisms in other disease models.

Cascade signal amplification strategy for subattomolar protein detection by rolling circle amplification and quantum dots tagging

A cascade signal amplification strategy was proposed for detection of protein target at ultralow concentration by combining the rolling circle amplification (RCA) technique with oligonucleotide functionalized quantum dots (QDs), multiplex binding of the biotin-strepavidin system, and anodic stripping voltammetric detection. The RCA product containing tandem-repeat sequences could serve as excellent template for periodic assembly of QDs, which presented per protein recognition event to numerous quantum dot tags for electrochemical readout. Both the RCA and the multiplex binding system showed remarkable amplification efficiency, very little nonspecific adsorption, and low background signal. Using human vascular endothelial growth factor as a model protein, the designed strategy could quantitatively detect protein down to 16 molecules in a 100 microL sample with a linear calibration range from 1 aM to 1 pM and was amenable to quantification of protein target in complex biological matrixes. The proposed cascade signal amplification strategy would become a powerful tool for proteomics research and clinical diagnostics.

A high-performance VEGF aptamer functionalized polypyrrole nanotube biosensor

In this study, we examined the in vitro electrochemical detection of Vascular Endothelial Growth Factor (VEGF) as cancer biomarker using p-type field-effect transistor (FET) biosensor. We demonstrated the high-performance FET sensor, which could detect ca. 400 fM of VEGF concentration, based on anti-VEGF RNA aptamer conjugated carboxylated polypyrrole nanotubes (CPNTs). The CPNTs used as high-performance transducers of this FET system were successfully fabricated by cylindrical micelle templates in a water-in-oil emulsion system. The functional carboxyl group (-COOH) was effectively incorporated into the polymer backbone during the polymerization by using pyrrole-3-carboxylic acid (P3CA) as a co-monomer. Two types of CPNTs (CPNT1: ca. 200 nm in diameter, CPNT2: ca. 120 nm in diameter) demonstrated the excellent conductivity performance in this FET system. Based on CPNTs conjugated with anti-VEGF RNA aptamer (CPNTs-aptamer), VEGF (target molecule) acts as the gate dielectrics of p-type FET sensor and specifically interacts with anti-VEGF aptamer attached to CPNT surfaces. Importantly, the VEGF detection limit of the FET sensor based on CPNT2-aptamer was found to be near 400 fM in real-time. Moreover, the CPNTs-aptamer FET sensors can be repeatedly used for various concentrations of the target molecule (VEGFs) through the washing and rinsing processes.