Ansuman Banerjee

A Polarization Isolation Method for High-Sensitivity, Low-Cost On-Chip Fluorescence Detection for Microfluidic Lab-on-a-Chip

The trend in medical equipment is toward compact and integrated low-cost medical test devices. Fluorescence-based assays are used to identify specific pathogens through the presence of dyes, but typically require specialized microscopes and narrowband optical filters to extract information. We present a novel, high-sensitivity, cost-effective, cross-polarization scheme to filter out excitation light from a fluorescent dye emission spectrum. This concept is demonstrated using an inverted microscope fitted with a halide lamp as the excitation source and an organic photo voltaic (organic photodiode) cell as the intensity detector. The excitation light is linearly polarized and used to illuminate a microfluidic device containing a 1 volume of dye dissolved in ethanol. The detector is shielded by a second polarizer, oriented orthogonally to the excitation light, thus reducing the magnitude of the detector photocurrent by about 25 dB. The signal due to fluorescence emission light, which is randomly polarized, is only attenuated by about 3 dB. As proof-of-principle, the fluorescence signal from the dyes Rhodamine 6G (emission wavelength of 570 nm) and Fluorescein (emission wavelength 514 nm) are measured in a dilution series with resulting emission signal being detected by an organic photodiode. Both dyes were detectable down to concentrations of 10 nM. This suggests that an integrated microfluidic device, with an organic photodiode and an organic light emitting excitation source and integrated polarizers, could be fabricated to realize compact and economical lab-on-a-chip devices for point-of-care diagnostics and on-site analysis.

On-chip fluorescence detection with organic thin film devices for disposable lab-on-a-chip sensors

In this paper, we present an improved high-sensitivity approach for on-chip fluorescence-based measurements for disposable lab-on-a-chip (LOC). The approach is based on using an organic LED for excitation and an organic photodiode (OPD) as detector. By enhancing device integration with a custom interconnect, optical losses were minimized and the signal-to-noise ratio was increased. Using a bi-layer OPD improved detector responsivity 10 times over the conventional single heterojunction OPD. Finally, a lock-in amplifier was used instead of direct current measurements. Combining advantages of these improvements, a limit of detection of 10 nM was demonstrated, which is a 10-fold improvement over our previous reports and a 100-fold improvement over reports by others. We expect the developed approach to envisage numerous applications in point-of-care (POC) diagnostics and on-site environmental testing.

High Sensitivity On-Chip Fluorescence Detection Based on Cross-Polarization and Thin-Film Organic Photodetectors

In this paper we present a novel, high-sensitivity, cost-effective cross-polarization scheme to filter out excitation light from a fluorescent dye emission spectrum. With this scheme, it is possible to achieve a detection limit of 10 nM which is a 1,000 fold reduction from previously published results. The concept is demonstrated using an inverted microscope with a halide lamp as the excitation source and an organic photodiode as the intensity detector. The excitation light is linearly polarized and used to illuminate a microfluidic device containing 1 muL of Rhodamine 6G dye dissolved in ethanol. The detector is shielded by a second polarizer, orientated orthogonally to the excitation light. The resulting emission signal was detected by the organic photodiode down to a concentration of 10 nM. This scheme opens the possibility to fabricating integrated microfluidic devices with fluorescence detection, suitable for point- of-care (POC) diagnostics, biomedical and environmental applications.

Epoxyless Fiber-to-Submount Bonding for Active Fiber Optoelectronic and Fiber Backplane Applications

A fiber-coupled optical transmitter or receiver is both a mechanical and an optical system. Packaging of optical components like fiber-coupled lasers requires good coupling into the fiber, and rigid inflexible mounting of all components, so the coupling remains stable over the multiyear lifetime expected of optoelectronic components. In this paper, we report a new technique for bonding fiber directly to a Si or glass submount for autoaligned direct fiber attachment, based on field-assisted anodic or cathodic bonding. Under the influence of an electric field at high temperature, oxides are formed between the glass and the metal: this method is used to bond both metallized fibers to a glass V-groove (cathodic bonding), and glass fibers to a metallized Si submount (anodic bonding), without epoxy. Typical shear strengths are >300 g, comparable to solder-mounted components. The V-grooves precisely align the fiber to the component in two of the three dimensions. The thermal stability of this technique is demonstrated through showing <0.1 dB variation in coupling between two bonded fibers in aV-groove over a temperature range of 25degC-85degC. This method of fiber attachment is a robust and economical way to attach fibers for passive alignment and direct butt-coupling between the fiber and the semiconductor laser, receiver, or other optoelectronic component

On-Chip Fluorescence Detection Using Organic Thin Film Devices for a Disposable Lab-on-a-Chip

In this paper, we present a high-sensitivity approach for on-chip fluorescence-based measurements for disposable lab-on-a-chip (LOC) with an integrated organic light-emitting diode (OLED) excitation source and organic photodiode (OPD) detector. A simple and inexpensive cross- polarization scheme was used to filter out excitation light from the fluorescent dye emission spectrum. We incorporated a bi- layer OPD detector with responsivity 10 times higher than conventional single heterojunction OPD, resulting in a detection limit of 1 nM, which is a 1,000-fold improvement over previous publications. The dynamic experiment was conducted and the result shows promising application in realtime fluorescence analysis. The demonstrated on-chip fluorescence detection approach is ideally suited for integration with disposable LOC devices for point-of-care diagnostics and on-site environmental testing.