Hollow-core photonic Bragg fibers have a wide range of sensing applications.In this paper,a hollow-core photonic Bragg fiber with defect layers is proposed and analyzed for bacterium detection in the terahertz (THz) frequency range.The hollow core of the fiber is surrounded by a periodic sequence of high/low refractive index (RI) multilayers including the photosensitive resin and air.The analytes are deposited on the inner surface of the THz hollow-core Bragg fiber to induce the defect layer.The performance of the proposed surface bio-sensor is numerically investigated.The result shows that the proposed surface bio-sensor provides a high core power fraction.The confinement loss of the proposed surface bio-sensor takes on two peaks in the frequency range of 0.3—0.4 THz and 0.45—0.55 THz,respectively.The distinguishable characteristic frequencies of the proposed surface bio-sensor are obtained with different bacterium deposited on the inner surface of the THz Bragg fiber which can be used to recognize the kind of the bacterium.Furthermore,the thickness-independent surface sensing can be realized in the high frequency range.The proposed surface bio-sensor based on THz hollow-core Bragg fiber can be used to recognize the kind of the bacterium and has a great potential in microorganism detections.