Reducing cost and time is a major concern in clinical diagnostics. Current molecular diagnostics are multi-step processes that usually take at least several hours or even days to complete multiple reagents delivery, incubations and several washing processes. This highly labor-intensive work and lack of automation could result in reduced reliability and low efficiency. The Laboratory-on-a-chip (LOC), taking advantage of the merger and development of microfluidics and biosensor technology, has shown promise towards a solution for performing analytical tests in a self-contained and compact unit, enabling earlier and decentralized testing. However, challenges are to integrate the fluid regulatory elements on a single platform and to detect target analytes with high sensitivity and selectivity. The goal of this research work is to develop an AC electrokinetic (ACEK) flow through concentrator for in-situ concentration of biomolecules and develop a comprehensive understanding of effects of ACEK flow on the biomolecule transport (in-situ concentration) and their impact on electronic biosensing mechanism and performance, achieving automation and miniaturization. ACEK is a new and promising technique to manipulate micro/bio-fluids and particles. It has many advantages over other techniques for its low applied voltage, portability and compatibility for integration into lab-on-a-chip devices. Numerical study on preconcentration system design in this work has provided an optimization rule for various biosensor designs using ACEK technique. And the microfluidic immunoassay lab-chip designed based on ACET effect has showed promising prospect for accelerated diagnostics. With optimized design of channel geometry, electrode patterns, and properly selected operation condition (ac frequency and voltage), the preconcentration system greatly reduced the reaction time to several minutes instead of several hours, and improved sensitivity of the assay. With the design of immunoassay lab-chip, one can quantitatively study the effect of ACET micropumping and mixing on molecular level binding. Improved sensors with single-chip form factor as a general platform could have a significant impact on a wide-range of biochemical detection and disease diagnostics including pathogen/virus detection, whole blood analysis, immune-screening, gene expression, as well as home land security.