UV-Vis spectrophotometry based on absorption spectrometry is widely used for the analysis of organic compounds.Traditional spectrophotometers with silicon cuvettes are unsuitable for the high-throughput detection of precious biological samples due to the complicated operation and large consumption of samples,usually tens of m icroliters or more.Here we constructed an optical fiber biosensor for the UV spectrophotometric detection of micro-nano-liter biological samples.The biosensor was comprised of seven optical fibers of 400μm in diameter.Two approaches of the detection system,namely central-fiber-illumination and surrounding-fibers-collection,in contrast to surrounding-fibers-illumination and central-fiber-collection,were both evaluated by measuring the concentrations of single-stranded DNA samples in trace volume.The result showed that the method based on central-fiber-illumination and surrounding-fibers-collection gives higher accuracy,and the linear range of the optical fiber biosensor is 1-1000 ng/μL,the sensitivity 1 ng/μL and the reproducibility ±2%.The sample consuming in all detections is 1 μL or even less.Compared with the current commercial instruments,our fiber opt-biosensor system exhibits some special advantages besides the high performance.First,less sample consuming is required,which is crucial for precious biological samples detection.Moreover,our fiber opt-biosensor system is with a very simple structure,which has loose requirement for manufacturing precision and lower cost of the instrument.In addition,opening detection window is more suitable for the integration in Micro Total Analysis Systems or Lab-On-A-Chip.