Dispersion compensated optical amplifier in Ti-diffused PPLN ridge waveguide.

Nonlinear optical phase conjugation is known to be an effective technique for dispersion compensation in optical fibers. It requires an optical filter to separate out only the phase conjugated signal at the output to achieve signal pulse re-narrowing by its subsequent propagation through an identical medium. In this paper, a compact design, which integrates the optical phase conjugator and the filter on a single substrate of periodically poled lithium niobate and facilitates the use of a single pump source for both phase conjugation and amplification, is proposed and analyzed using computer simulations.

A new approach towards the Debye length challenge for specific and label-free biological sensing based on field-effect transistors.

Biologically-modified field-effect transistors (BioFETs) are promising platforms for specific and label-free biosensing due to their sub-micron footprint suitable for multiplexing in ultra-small samples, low noise levels, inherent amplification, etc. Debye screening length is a well-recognized challenge for any BioFET-based technology. The screening length is the smallest at the double layer, where the solution ion population is higher than the bulk population. One way to address the small double layer screening length is to electrostatically modify the potential drop across the solution such as to minimize the potential drop over the double layer. This will decrease the population of the double layer ions and increase the screening length. However, this is not possible with BioFETs as voltage application to the reference electrode simultaneously affects both the double layer and the BioFET conducting channel. The current study addresses the screening length challenge with the novel Meta-Nano-Channel (MNC) BioFET. The MNC BioFET, which is fabricated in a complementary-metal-oxide-silicon (CMOS) process, allows decoupling of the electrostatics of the double layer from the electrodynamics of the conducting channel. The study explores the mechanism of sensing with the MNC BioFET, and demonstrates how the double layer can be electrostatically tuned in order to optimize the screening length without affecting the conducting channel. Finally, specific and label-free sensing of 10 ng ml-1 prostate specific antigen (PSA) is demonstrated. It is shown that by electrostatically increasing the double layer screening length, the sensing signal increases from 70 mV to 133 mV.

Electrostatically Governed Debye Screening Length at the Solution-Solid Interface for Biosensing Applications.

Biosensors based on field-effect devices (bioFETs) offer numerous advantages over current technologies and therefore have attracted immense research over the decades. However, short Debye screening length in highly ionic physiological solutions remains the main obstacle for bioFET realization. This challenge becomes considerably more acute at the electrolyte-oxide interface of the sensing area due to high ion concentration induced by the charged amphoteric sites, which prohibits any attempt to employ the field-effect mechanism to "sense" any charged biomolecules. In this work, we present an electrostatic approach by which the double layer (DL) excess ion concentration is removed, thus forcing the DL ion concentration to match the bulk concentration, which subsequently forces bulk screening length at the DL, thereby "exposing" target biomolecules to the underlying bioFET. To this end, we employ local tunable surface electric fields, introduced to the DL using surface passivated-metal electrodes. We examine numerically and analytically the effect of these electric fields on the DL ion distribution. We also numerically demonstrate the feasibility of the proposed approach for a fully depleted silicon-on-insulator based bioFET and show how the threshold voltage shift induced by the presence of target molecules increases by almost two orders of magnitude upon the removal of the surface excess ion population.

Specific and label-free immunosensing of protein-protein interactions with silicon-based immunoFETs.

The importance of specific and label-free detection of proteins via antigen-antibody interactions for the development of point-of-care testing devices has greatly influenced the search for a more accessible, sensitive, low cost and robust sensors. The vision of silicon field-effect transistor (FET)-based sensors has been an attractive venue for addressing the challenge as it potentially offers a natural path to incorporate sensors with the existing mature Complementary Metal Oxide Semiconductor (CMOS) industry; this provides a stable and reliable technology, low cost for potential disposable devices, the potential for extreme minituarization, low electronic noise levels, etc. In the current review we focus on silicon-based immunological FET (ImmunoFET) for specific and label-free sensing of proteins through antigen-antibody interactions that can potentially be incorporated into the CMOS industry; hence, immunoFETs based on nano devices (nanowire, nanobelts, carbon nanotube, etc.) are not treated here. The first part of the review provides an overview of immunoFET principles of operation and challenges involved with the realization of such devices (i.e. e.g. Debye length, surface functionalization, noise, etc.). In the second part we provide an overview of the state-of-the-art silicon-based immunoFET structures and novelty, principles of operation and sensing performance reported to date.