Miniature Planar Nuclear Magnetic Resonance Probe Based On Digital Microfluidic Technology

Nuclear magnetic resonance is a commonly used technique in chemical analysis,but its low sensitivity has greatly restricted its further development and application in the field of micro-sample detection and in-situ reaction monitoring.There are currently three mainstream solutions for low sensitivity:enhancing the strength of the electrostatic field,hyperpolarization,using micro-coils.Using micro-coils in the above three solutions is more feasible and easier to save production costs.To solve the above problems,this paper designs and manufactures a digital microfluidic system suitable for high-field nuclear magnetic resonance spectrometers,and builds a matching miniature planar coil probe.The digital microfluidic system mainly includes digital microfluidic chip,droplet drive circuit,Miniature planar ring coil,3D printing probe holder,tuning matching circuit and other parts.The digital microfluidic chip is made of transparent ITO glass,which carries different kinds of samples and provides a place for movement and reaction.Using the drive circuit made of STM32,it can remotely control the chip voltage according to the instructions of the host computer,and drive a variety of sample droplets to move and mix.The in-situ monitoring of trace samples is carried out by a specially designed miniature planar coil probe.The micro-coil is designed with a planar ring structure and is processed and manufactured with a low-loss Teflon FR-4 PCB high-frequency circuit board.The specific size and structure of the coil are optimized by CST numerical simulation to make it more suitable for the detection requirements of the microfluidic chip in this paper.The generated radio frequency field has higher intensity and better uniformity in the detection area of the trace sample.In order to verify the usability of the design,we used the system to react with aldamine reaction(sodium benzaldehyde-2-sulfonate and aniline)and photopolymerization(polyethylene glycol ester(PEG-DA))In-situ detection was carried out,and a clearer 1H NMR spectrum can be collected during the in-situ detection experiment.The experimental results prove the usability of the design in this paper.The combination of DMF and NMR provides a new and powerful tool for in-situ reaction monitoring of trace samples,and has a wide range of applications in the field of chemical analysis.