Detection of Hepatitis B Virus (HBV) DNA at femtomolar concentrations using a silica nanoparticle-enhanced microcantilever sensor

MEMS biosensor for detection of Hepatitis A and C viruses in serum

Resonant microcantilever arrays are developed for the purpose of label-free and real-time analyte monitoring and biomolecule detection. MEMS cantilevers made of electroplated nickel are functionalized with Hepatitis antibodies. Hepatitis A and C antigens at different concentrations are introduced in undiluted bovine serum. All preparation and measurement steps are carried out in the liquid within a specifically designed flowcell without ever drying the cantilevers throughout the experiment. Both actuation and sensing are done remotely and therefore the MEMS cantilevers have no electrical connections, allowing for easily disposable sensor chips. Actuation is achieved using an electromagnet and the interferometric optical sensing is achieved using laser illumination and embedded diffraction gratings at the tip of each cantilever. Resonant frequency of the cantilevers in dynamic motion is monitored using a self-sustaining closed-loop control circuit and a frequency counter. Specificity is demonstrated by detecting both Hepatitis A and Hepatitis C antigens and their negative controls. This is the first report of Hepatitis antigen detection by resonant cantilevers exposed to undiluted serum. A dynamic range in excess of 1000 and with a minimum detectable concentration limit of 0.1ng/ml (1.66pM) is achieved for both Hepatitis A and C. This result is comparable to labeled detection methods such as ELISA.

Surface modification and biomolecule immobilization on polymer spheres for biosensing applications

Microspheres and nanospheres are being used in many of today's biosensing applications for automated sample processing, flow cytometry, signal amplification in microarrays, and labeling in multiplexed analyses. The surfaces of the spheres/particles need to be modified with proteins and other biomolecules to be used in these sensing applications. This chapter contains protocols to modify carboxyl- and amine-coated polymer spheres with proteins and peptides.

Analysis of DNA hybridization regarding the conformation of molecular layer with piezoelectric microcantilevers

Lead Zirconate Titanate (PZT)-embedded microcantilevers were fabricated with dimensions of 30 × 90 × 3 μm(3) (width × length × thickness). A thicker PZT layer improved the actuation and enabled long-term data acquisition in common aqueous buffers with a frequency resolution of 20 Hz. A quantitative assay was conducted in the range of 1-20 μM and the resonant frequency was found to increase with the concentration of target DNAs and the probe DNAs were almost saturated at 20 μM. Back-filling with ethyleneglycol-modified alkanethiol was shown to facilitate the hybridization efficiency and stabilize the surface reaction, resulting in a signal enhancement of 40%. We report for the first time how secondary structures in oligonucleotide monolayer change the surface property of a dynamic mode microcantilever and subsequently affect its oscillating behavior. Using fabricated microcantilevers, the real time changes in resonant frequency upon hybridization were measured by utilizing different probe and target sets. The results revealed that the microcantilevers experienced a resonant frequency upshift during the hybridization with complementary DNAs if a dimer structure was present between DNA probes. A resonant frequency downshift was observed for DNA probes that did not contain any complex secondary structures. In addition, the results demonstrate the potential of using these microcantilevers to extract structural information of oligonucleotides.