Surface plasmon biosensors provide label-free and sensitive bio-detections. However, how to achieve a biochip with low-cost, high-throughput and ultra-sensitivity is an important issue. We introduce the fabrication of nanoslit arrays by using electron-beam lithography and nanoimprint technology. The surface plasmon resonances in gold nanoslits are applied for microarray detections. The experimental results show the sensitivity is greatly enhanced by reducing the slit width. The detection limit for anti-BSA protein is up to 35pM.