Femtosecond Laser Ablated Optical Fiber SERS Sensor And Its Preliminary Application In DNA Detection

Traditional surface-enhanced Raman scattering?SERS?substrates are prepared by fabricating noble metal nanostructures on glass or silicon substrates.Traditional SERS spectral detection needs to detect the analyte on the substrate,which can not meet the practical application in remote,in situ,in vivo and dangerous environment.However,Optical fiber has the advantages of large aspect ratio and good flexibility,which make it can be applied on remote detection.Optical fiber SERS sensor,as a combination of optical fiber sensor and SERS spectrum detection technology,enables remote,in-situ and real-time SERS spectrum detection to be realized,and avoids the problem of space beam interference when using traditional SERS substrate detection.In this paper,the fabrication and application of optical fiber SERS sensor are explored in the following aspects:1.In this paper,a flat-end SERS fiber probe?FSP?is prepared and its performance is studied.The femtosecond laser ablation is used to roughen the end surface of the quartz multimode fiber,silver nanostructures are deposited on that rough end of the fiber by laser-induced deposition,to realize the flat-end SERS probe.Using Rhodamine 6G?R6G?as target molecule,the remote Raman spectrum detection was realized by FSP.The mechanism of laser-induced deposition of silver particles is analyzed theoretically.In order to optimize the sensitivity and repeatability of flat-ended SERS fiber probes,two parameters,induced power ratio and ablation pulse energy of femtosecond laser,were introduced and optimized.The experimental results show that 50%is the optimum induced power ratio and 0.24?J is the optimum energy of single laser pulse.For R6G solution,the sensitivity of the FSP with optimized parameters is about 20 times of the non-laser ablated multimode fiber SERS probe,which proves that femtosecond laser ablation can improve the enhancement factor of the optical fiber SERS sensor.2.A highly sensitive pyramid-shaped SERS fiber probe?P-Probe?has been first realized by fabrication method-femtosecond?fs?laser ablation.The pyramid-shaped optical fibers is programmatically fabricated with 0.54?J laser pulse energy.With Rhodamine 6G being target molecules,the performances of P-Probes prepared at different induction power ratios?40%,50%,60%,70%and 80%?were discussed.The experimental results show that,the induction power ratio 60%is the optimized value for the enhancement of SERS signal.And the detection limit of the fiber SERS probe is down to 10^-9M,the Raman enhancement factor of the P-Probes fabricated with the optimum induced power ratio?60%?is 10⁷.This P-Probes can be an alternative tool to detect the biomolecules of a single cell in biology sensing applications.3.In this paper,the flat-end quartz SERS fiber probe is applied to detect the gene fragment of deafness.The molecular beacon of deafness gene fragment is fixed on the SERS substrate of FSP by Ag-S bond to construct a flat-end fiber SERS gene probe?DAF?.To study the performance of DAF,this experiment attempt to detect different DNA sequences in solution with DAF.It comes out that DAF,a gene probe using the SERS signal descent of dye molecule to identify target sequence,has the ability to qualitatively identify deaf genes solution with concentration above 10^-9M.While the detection of DNA solution with concentration below 10^-10M needs to further optimize the sensitivity of FSP and the repeatability of DAF.