Composition and methods for amplifying and detecting solution-state polynucleotide targets in a single device are described. In one aspect, a method for a coupled isothermal amplification and detection process utilizes a coated solid support, including a solid substrate, a cationic layer, and a plurality of target-specific probes attached to the coated solid support. Polynucleotide targets in the sample are amplified by an isothermal amplification process involving in situ hybridization onto the coated solid support. The entire process can be carried out with a high degree of specificity under low salt conditions in less than one hour. Further aspects of the present invention include methods for coupled hybridization/detection of polynucleotide targets, coated silicon biosensors optimized for use with the coupled detection systems to provide visual detection of polynucleotide targets under visible light conditions, and kits for practicing in the above described methods.