A method for DNA-based detection of E. coli O157:H7 in a proteinous background using piezoelectric-excited cantilever sensors.

We show for the first time the detection of ~700 E. coli O157:H7 (EC) in both buffer and proteinous sample (beef wash) using the virulent gene stx2 as a sensing molecule immobilized on piezoelectric-excited millimeter cantilever (PEMC) sensors without a sample preparation step. Genomic DNA of EC suspended in buffer or beef wash was extracted using a 30-minute procedure, or using a commercial extraction kit, and then was exposed to the sensor immobilized with a 19-mer probe that is complement to stx2 gene.

PEMC-based method of measuring DNA hybridization at femtomolar concentration directly in human serum and in the presence of copious noncomplementary strands.

Piezoelectric-excited, millimeter-sized cantilever (PEMC) sensors having high-mode resonance near 1 MHz are shown to exhibit mass change sensitivity of 1-300 ag/Hz. Gold-coated PEMC sensors immobilized with 15-mer single-stranded DNA (ssDNA) were exposed to 10-mer complementary strands at concentrations of 1 fM, 1 pM, and 1 microM, both separately and sequentially at 0.6 mL/min in a sample flow cell housing the sensor.

Method for measuring the self-assembly of alkanethiols on gold at femtomolar concentrations.

We describe a cantilever-based method for measuring the self-assembly of alkanethiols on a gold surface in a flow system that permits easy step changes in concentration and acquire a continuous in situ measure of the resulting chemisorption through the change in resonance frequency. A gold-coated (2.2 mm2), piezoelectric-excited, millimeter-sized cantilever (PEMC) sensor was exposed to 1-hexadecanethiol (HDT) in ethanol at concentrations ranging from 1 fM to 1 mM, sequentially and separately.

Method for label-free detection of femtogram quantities of biologics in flowing liquid samples.

Rapid (approximately 10 min) measurement of very low concentration of pathogens (approximately 10 cells/mL) and protein (approximately fg/mL) has widespread use in medical diagnostics, monitoring biothreat agents, and in a broader context as a research method. For low-level pathogen, we currently use culture enrichment methods and, thus, rapid analysis is not possible. For low protein concentration, no direct method is currently available.

Effects of geometry on transmission and sensing potential of tapered fiber sensors.

Geometry of tapered fiber sensors critically affects the response of an evanescent field sensor to cell suspensions. Single-mode fibers (nominally at 1300 nm) were tapered to symmetric or asymmetric tapers with diameters in the range of 3-20 microm, and overall lengths of 1-7 mm. Their transmission characteristics in air, water and in the presence of Escherichia coli (JM101 strain) at concentrations of 100, 1000, 7000 and 7 million cells/mL were measured in the 400-800 nm range and gave rich spectral data that lead to the following conclusions.

Detection of pathogen Escherichia coli O157:H7 AT 70 cells/mL using antibody-immobilized biconical tapered fiber sensors.

Optical fibers (core diameter 8 microm, cladding diameter 125 microm) was tapered to a waist diameter in the range of 8-12 microm, and then a monoclonal antibody to the pathogen, Escherichia coli O157:H7 was covalently bonded to the surface of the tapered region. Using 470 nm light, the taper was exposed to various concentrations (7 x 10(7), 7 x 10(5), 7 x 10(3), and 70 cells/mL) of the pathogen, and the sensor showed changes in transmitted light as the antigen attached to the antibody on the taper surface. The response was equal and opposite when the pathogen was released from the surface using a low pH buffer.