This paper reports the design, fabrication and testing of a microfluidic based impedance biosensor for rapid and simultaneous detection of three Salmonella serogroups. The microfluidic device consists of three microchannels, each one includes a region for focusing the Salmonella cells into the centerline of the microchannel and direct them toward the sensing region to obtain highly concentrated samples using positive dielectrophoresis force. A region for bacteria sensing consists of interdigitated electrode (IDE) array with 10 pairs of fingers. Three types of Salmonella antibodies (type B, D and E) were mixed separately with the cross-linker (Sulfo-LC-SPDP) to enhance the immobalization of the antibodies to the detection electrodes. The electrode surfaces was then functionalized with the three mixtures, one for each channel. As target antigen binds to the antibody, it results in impedance change. The Salmonella samples were spiked with Salmonella type B, introduced into the biosensor via the sample inlet into the focusing region, and then toward the sensing region where they bind to the immobilized antibody, causing a change in the impedance. The performance of the devices was tested using single Salmonella serotype B and two Salmonella serotypes B, and D, with a limit of detection of 7 cells/ml. The biosensor was also able to differentiate live from dead bacteria eliminating the false positive results. Finally, the device was also able to detect Salmonella selectively when other type of pathogen was present.

A MEMS-based impedance biosensor was designed, fabricated, and tested to effectively detect the presence of bacterial cells including E. coli O157:H7 and Salmonella typhimurium in raw chicken products using detection region made of multiple interdigitated electrode arrays. A positive dielectrophoresis based focusing electrode was used in order to focus and concentrate the bacterial cells at the centerline of the fluidic microchannel and direct them toward the detection microchannel. The biosensor was fabricated using surface micromachining technology on a glass substrate. The results demonstrate that the device can detect Salmonella with concentrations as low as 10 cells/mL in less than 1 h. The device sensitivity was improved by the addition of the focusing electrodes, which increased the signal response by a factor between 6 and 18 times higher than without the use of the focusing electrodes. The biosensor is selective and can detect other types of pathogen by changing the type of the antibody immobilized on the detection electrodes. The device was able to differentiate live from dead bacteria.

In this study, numerical modeling of nonlinear dynamic responses of miniature electromagnetic energy harvesters is reported for multiple impacts using limited amplitude and low-frequency excitations (0.5–3 g, 10–40 Hz). When an external vibration source frequency approaches oscillators’ resonate frequencies (15 Hz and 30 Hz), these oscillators strongly impact onto a stiffer cantilever resulting in a much higher frequency vibration (1 kHz) in accordance with a large frequency up-conversion factor ∼33.3–66.6. The Lorentz force and the nonlinear oscillators together resulted in complicated nonlinear dynamic responses of the cantilever, such as period doubling, superharmonic, or chaotic. Furthermore, the instantaneous generated power of miniature electromagnetic harvester was dramatically enhanced with 3 μW, and the enhancement came from the more the number of oscillators, the lesser the air damping, and appropriate frequencies from external vibration sources. Moreover, the free tip of the cantilever in the system with both of the cube nonlinear oscillators and the linear oscillators were carefully analyzed by the phase portraits to demonstrate its dynamic responses behavior.

This paper reports the design, fabrication, and testing of a microfluidic MEMS biosensor for rapid sensing of low concentration Escherichia coli O157:H7. It consists of a specially designed focusing and sensing region, which enables the biosensor to detect low concentration of bacterial cells. The focusing region consists of a ramped vertical electrode pair made of electroplated gold along with tilted thin film finger pairs (45°) embedded inside a microchannel. The focusing region generates positive dielectrophoresis force, which moves the cells towards the edges of the tilted thin film electrode fingers, located at the center of the microchannel. The fluidic drag force then carries the focused cells to the sensing region, where three interdigitated electrode arrays (IDEAs) with 30, 20, and 10 pairs, respectively, are embedded inside the microchannel. This technique resulted in highly concentrated samples in the sensing region. The sensing IDEAs are functionalized with the anti-E. coli antibody for specific sensing of E. coli 0157:H7. As E. coli binds to the antibody, it results in an impedance change, which is measured across a wide frequency range of 100 Hz-10 MHz. The biosensor was fabricated on a glass substrate using the SU8 epoxy resist to form the microchannel, gold electroplating to form the vertical focusing electrode pair, a thin gold film to form the sensing electrode, the finger electrodes, traces and bonding pads, and polydimethylsiloxane to seal the device. The microfluidic impedance biosensor was tested with various low concentration bacterial samples and was able to detect bacterial concentration, as low as 39 CFU/ml with a total sensing time of 2 h.

This paper reports the design, fabrication and characterization of an impedance based biosensor for simultaneous detection of three Salmonella serogroups (type B, D, and E), with low concentration in ready to eat Turkey matrix. The measurements demonstrate that the device can selectively detect Salmonella, e.g., type B at a concentration as low as 8 cell/ml with a detection time of 1 hour. The addition of focusing region has improved the signal strength by a factor ranged between 4. The antibody immobilization on top of the detection electrodes was studied as a function of time between 0.5 - 3 hours. The results demonstrate that an optimized coating can be achieved within 1.5 hours at 1X antibody coating. The design has shown a significant improvement in capability to detect Salmonella compared to traditional culture methods, PCR and ELISA based detection.

We present a low cost, easy to fabricate biosensor, which can quickly and accurately detect Salmonella typhimurium. This study also compares the advantages of the microfluidic biosensor over a nonmicrofluidic biosensor. High density interdigitated electrode array was used to detect Salmonella cells inside a microfluidic chip. Monoclonal anti-Salmonella antibodies were allowed to be immobilized on the surface of the electrode array for selective detection of Salmonella typhimurium. An impedance analyzer was used to measure and record the response signal from the biosensor. The biosensor provides qualitative and quantitative results in 3 hours without any enrichment steps. The microfluidic biosensor’s lower detection limit was found to be 3×103 CFU/mL compared to the 3×104 CFU/mL of the nonmicrofluidic biosensor, which shows that the microfluidic biosensor has 10-fold increased sensitivity. The impedance response of microfluidic biosensor was also significantly higher (2 to 2.9 times) compared to the nonmicrofluidic biosensor.

We show that inline silicon waveguides inside a laser cavity facilitate laser modelocking due to TPA and TPA-induced FCA, and it can also provide Raman amplification and dual wavelength lasing in the same silicon waveguide.

We demonstrate dual-wavelength short pulses lasing at 1540 and 1675 nm based on a silicon waveguide. The inline silicon waveguide inside a laser cavity facilitates pulse compression and laser mode-locking due to two-photon absorption (TPA) and TPA-induced free-carrier absorption at 1540 nm. Compressed pulses provide pump for stimulated Raman scattering. Raman amplification and low threshold Raman lasing are observed based on the same silicon waveguide.

An experimental investigation on noise performances of supercontinua generated in normal and anomalous dispersion fibers is carried out. The supercontinuum in the normal dispersion fiber has lower real time amplitude noise and timing jitter.

A numerical investigation on noise figure (NF) inside the silicon waveguides pumped with high-repetition-rate pulses is carried out. The parameters of pump pulses are important to generate net gain and <7dB NF in silicon waveguides.

FCA can be used as pulse compressor if it exceeds TPA at the pulse center by using sharper pulses or higher peak powers. Tripling rise time requires 7 dB more power to achieve 80 ps output pulses.

A novel pulse compression and modelocking scheme by using TPA and TPA induced free carrier absorption in silicon waveguides is demonstrated. Experimentally we obtain 12 fold pulse compression and 85ps modelocked pulses at 1550nm.

Aggregate nonlinear response of silicon is determined by the competition between the free carrier absorption (FCA) and two-photon absorption (TPA). We show that the front end of optical pulses is always exposed to TPA dominated nonlinear regime, whereas the trailing edge can be seen at FCA dominated regime at high intensities. These two losses can be used for pulse compression if the center of the pulse is in FCA dominated nonlinear regime. To reach this operation regime, energy of 50ps wide pulses has to be larger than 50nJ (40GW∕cm2). Competition phenomenon is observed experimentally in a mode locked laser setup to generate 60ps pulse of 60nJ.