Halloysite Nanotubes Modified Surface Plasmon Resonance Sensor

Surface Plasmon Resonance(SPR)technology has been widely used in many fields,such as environmental monitoring,pesticide residue measurement,drug screening,food safety,medical diagnosis,etc.due to its intrinsic characteristics of anti-interference,label-free,and easy to build a setup system.Currently,SPR sensors are limited in their ability to detect small molecules with molecular weight less than 500 Da,ultra-low concentration substances,and substances with low binding affinity.Therefore,improving the sensitivity of SPR sensors is a significant issue in the field of bio-chemical sensing.In this paper,we proposed a method to modify surface SPR sensors with halloysite nanotubes(HNTs)and applied this method to prism-based and side-polished fiber(SPF)based SPR sensors.It is demonstrated that HNTs could enhance the refractive index sensitivity of the above two types of sensors.In addition,we also applied the modified sensors to the detection of phosphate buffer solution(PBS),bovine serum albumin(BSA)and human breast cancer cells(MCF-7).The results indicate that the HNTs-SPR sensors show high sensitivity and high capturing efficiency of tumor cells.The research results obtained in this paper are as follows:(1)HNTs modified prism-coupled SPR sensor.We fabricated a prism based sensor chip and modified the surface by spinning coating different concentrations of HNTs suspension.We obtained the optimal sensitivity of HNTs-SPR sensor by comparing the performance of the HNTs-SPR sensors with unmodified SPR sensors.The results show that the SPR sensor modified with the 7.5%HNTs suspension can achieve the best refractive index sensitivity of 10431 nm/RIU.This sensitivity is 5.6 times higher than that of the unmodified one and comes to the level of 10~4 nm/RIU.To the best of our knowledge,this is the first demonstration to utilize HNTs for achieving higher measurement sensitivity in SPR sensors.Also,we applied the modified SPR sensors in the detection of PBS,BSA,and MCF-7 cells.The results show that the HNTs-SPR sensors process high sensitivity for detection and high efficiency for capturing tumor cells.(2)HNTs modified SPF-SPR sensor.We fabricated the SPF-SPR sensor and modified it through spraying HNTs suspersion onto the gold surface.We found the optimal sensitivity of HNTs-SPF-SPR sensor by changing the concentration of sprayed HNTs.The experimental results show that the highest refractive index sensitivity is 11605nm/RIU when the 2.5%HNTs is sprayed,and its refractive index sensitivity is improved by 6.9 times compared with the unmodified one.At the same time,we also tested the modified sensor for the detection of PBS and BSA.We took full advantage of the real-time online detection of fiber-optic sensors and conducted continuous real-time detection of PBS and BSA.The SPF-SPR sensor shows enhanced sensitivity and holds high stability after the modification with HNTs.