The present invention relates to a method for concentrating a biological sample containing nucleic acids by using magnetic chitosan microparticles and subsequently performing a PCR reaction on the nucleic acids captured on the microparticles. The chitosan microparticles added to the biological sample at a PCR compatible pH are mechanically agitated to provide for cell lysis and simultaneous DNA capture, and then serve as a solid support for the nucleic acid template during the PCR reaction. As the chitosan microparticles are utilized for lysis and the nucleic acids do not need to be removed from the microparticles before PCR, the ease of the sample preparation procedure is dramatically improved.