Diagnostics based on point-of-care (POC) biosensors are essential for society, the environment, and human health. The current COVID-19 pandemic posted urgent requirements for developing portable biosensing systems for virus nucleic acid detection. Cellulose paper material-based biosensors feature low fabrication costs and versatile designs, suitable for different applications. This thesis aims to address the urgent diagnostic needs of COVID-19 infection by detecting the SARS-CoV-2 target genes with two paper-based systems. The first one is a smartphone-size portable system featuring a paper-based multi-well plate, operating based on the principle of isothermal amplification technique, Nucleic Acid Sequence Based Amplification (NASBA), and Toehold switch cell-free reaction. The developed portable system presented similar sensitivities to the same assay in the standard systems of a thermal cycler and a plate reader. The second one developed a paper-based chip and cassette operating with an oven for colorimetric reverse transcription-loop mediated isothermal amplification (RT-LAMP) reaction to detect the SARS- CoV-2 spike gene. The design of the wax-printed paper chip was studied for efficient nucleic acid amplification on the chip. Although showed lower sensitivity than the PCR tube-based amplification in a thermal cycler, the proposed RT-LAMP paper chip cassette is still promising to be further improved for decentralized nucleic acid tests. The work from this thesis is expected to generate practical impacts and can be extended for other viruses at the POC or point-of-need (PON) settings.