Abstract: A label free, reusable and high sensitivity viral fiber sensor is provided in the present invention. The label free, high sensitivity and reusability are the advantages of this sensor. Long Period Microfiber Grating (LPMFG) is used for the sensing device. It allows optically detecting the change in refractive index at the grating surface with an extra high sensitivity. This provides an optical detection method to monitor DNA Hybridization. The single stranded DNA (ssDNA) probe is immobilized onto the LPMFG's surface for hybridizing with a DNA sample in order to identify the viral strain in the sample. This LPMFG-based viral sensor functions by inducing a refractive index change on the grating surface through the bio-molecule binding between the target viral ssDNA and the immobilized probe ssDNA. Regeneration of a surface-immobilized probe without a significant loss of hybridization activity retains at least 10 successive assays without any significant loss of performance (less than 10% decrease).