Electrochemical quantification of DNA amplicons via the detection of non-hybridised guanine bases on low-density electrode arrays

Electrochemical primer extension for the detection of single nucleotide polymorphisms in the cardiomyopathy associated MYH7 gene

We report the labelling of dideoxy nucleotides (ddNTPs) for use in electrochemical array based primer extension for the detection of single nucleotide polymorphisms (SNPs). The results confirm the extension of the immobilised primers for each of the four ddNTPs, representing a significant advance in achieving a cost-effective platform for screening of disease-specific SNPs.

Graphene-mesoporous silica-dispersed palladium nanoparticles-based probe carrier platform for electrocatalytic sensing of telomerase activity at less than single-cell level

Human telomerase is a specialized ribonucleoprotein polymerase and is used as a clinical cancer marker and special target for chemotherapy. Traditional telomerase detection uses "telomerase repeat amplification protocol" (TRAP) assay. However, TRAP is questioned because it requires use of DNA polymerases, which is susceptible to polymerase chain reaction (PCR)-derived artifacts and time-consuming. Here, a novel PCR-free, electrocatalytic assay for signal-amplified detection of telomerase activity using graphene-mesoporous silica-dispersed palladium nanoparticles-based probe carrier platform to improve probe-target recognition is reported. The low background noise is achieved by using DNA site-specific cleavage endonuclease and the detection signal is amplified by using hemoglobin. As a highly efficient electron sink, hemoglobin does not carry out direct reduction at the surface, minimizing false positives. These merits make this assay highly sensitive, achieving the sensitivity comparable to TRAP. The developed electrocatalysis assay is PCR-free, simple in design, and fast in operation, therefore avoiding PCR amplification-related errors, which make it more reliable to evaluate telomerase activity for clinical use.

Electrical detection of dsDNA and polymerase chain reaction amplification

Food-borne pathogens and food safety-related outbreaks have come to the forefront over recent years. Estimates on the annual cost of sicknesses, hospitalizations, and deaths run into the billions of dollars. There is a large body of research on detection of food-borne pathogens; however, the widely accepted current systems are limited by costly reagents, lengthy time to completion, and expensive equipment. Our aim is to develop a label-free method for determining a change in DNA concentration after a PCR assay. We first used impedance spectroscopy to characterize the change in concentration of purified DNA in deionized water within a microfluidic biochip. To adequately measure the change in DNA concentration in PCR solution, it was necessary to go through a purification and precipitation step to minimize the effects of primers, PCR reagents, and excess salts. It was then shown that the purification and precipitation of the fully amplified PCR reaction showed results similar to the control tests performed with DNA in deionized water. We believe that this work has brought label free electrical biosensors for PCR amplification one step closer to reality.

Automated genotyping of circulating tumor cells

Cancer remains a prominent health concern in modern societies. Continuous innovations and introduction of new technologies are essential to level or reduce current healthcare spending. A diagnostic platform to detect circulating tumor cells (CTCs) in peripheral blood may be most promising in this respect. CTCs have been proposed as a minimally invasive, prognostic and predictive marker to reflect the biological characteristics of tumors and are implemented in an increasing number of clinical studies. Still, their detection remains a challenge as they may occur at concentrations below one single cell per ml of blood. To facilitate their detection, here we describe microfluidic modules to isolate and genotype CTCs directly from clinical blood samples. In a first cell isolation and detection module, the CTCs are immunomagnetically enriched, separated and counted. In a second module and after cell lysis, the mRNA is reversely transcripted to cDNA, followed by a multiplex ligation probe amplification of 20 specific genetic markers and two control fragments. Following the multiplex ligation probe amplification reaction, the amplified fragments are electrochemically detected in a third and final module. Besides the design of the modules, their functionality is described using control samples. Further testing using clinical samples and integration of all modules in a single, fully automated smart miniaturized system will enable minimal invasive testing for frequent detection and characterization of CTCs.

Design and testing of a packaged microfluidic cell for the multiplexed electrochemical detection of cancer markers

We present the rapid prototyping of electrochemical sensor arrays integrated to microfluidics towards the fabrication of integrated microsystems prototypes for point-of-care diagnostics. Rapid prototyping of microfluidics was realised by high-precision milling of polycarbonate sheets, which offers flexibility and rapid turnover of the desired designs. On the other hand, the electrochemical sensor arrays were fabricated using standard photolithographic and metal (gold and silver) deposition technology in order to realise three-electrode cells comprising gold counter and working electrodes as well as silver reference electrode. The integration of fluidic chips and electrode arrays was realised via a laser-machined double-sided adhesive gasket that allowed creating the microchannels necessary for sample and reagent delivery. We focused our attention on the reproducibility of the electrode array preparation for the multiplexed detection of tumour markers such as carcinoembryonic antigen and prostate-specific antigen as well as genetic breast cancer markers such as estrogen receptor-alpha, plasminogen activator urokinase receptor, epidermal growth factor receptor and erythroblastic leukemia viral oncogene homolog 2. We showed that by carefully controlling the electrode surface pre-treatment and derivatisation via thiolated antibodies or short DNA probes that the detection of several key health parameters on a single chip was achievable with excellent reproducibility and high sensitivity.

Lab-on-a-chip for the isolation and characterization of circulating tumor cells

A smart miniaturized system is being proposed for the isolation and characterization of circulating tumor cells (CTCs) directly from blood. Different microfluidic modules have been designed for cell enrichment and -counting, multiplex mRNA amplification as well as DNA detection. With the different modules at hand, future effort will focus on the integration of the modules in a fully automated, single platform.

Sensitivity enhancement in DNA hybridization assay using gold nanoparticle-labeled two reporting probes

A simple and sensitive method for DNA detection using gold nanoparticle (AuNP) two-probe detection system (AuNP-TP) was developed. Preliminary experiment was carried out by optimizing slide types, blocking agents and hybridization times. Fluorescent-labeled probes were used along with AuNP-labeled probes to confirm specific binding event between target DNA and probes. The sensitivities between AuNP single-probe (AuNP-SP) and AuNP-TP systems using sandwich-typed assay were compared. The AuNP-TP on epoxide-coated (EP) slides increased sensitivity 1000-fold at the detection limit of 100fM when compared to the AuNP-SP. This result indicates that the assay sensitivity was simply enhanced by simultaneous adding two AuNP labeled probes which selectively recognize different regions of the target DNA. The concept of AuNP-TP could potentially be applied to a macroarray format to detect multiple DNA targets simultaneously; thereby making the assay becomes more affordable and more sensitive.