Singapore-MIT Alliance for Research & Technology

BioSystems and Micromechanics (BioSyM) Inter-Disciplinary Research Group

Adhesive-based liquid metal radio-frequency microcoil for magnetic resonance relaxometry

The integration of microfabricated microcoil in a NMR system for bio-sensing has attracted a great deal of interest from the NMR research community. SMART BioSyM researchers and their collaborators have developed an Adhesive-based liquid metal radio-frequency microcoil for magnetic resonance relaxometry (MRR) Measurement. Conventionally, microcoils are fabricated by various techniques such as electroplating, microcontact printing and focused ion beam milling. These techniques require considerable fabrication efforts and incur high cost. In this work, a novel technique to fabricate three-dimensional multilayer liquid-metal microcoils together with the microfluidic network by lamination of dry adhesive sheets is demonstrated. Our liquidmetal microcoil has the highest quality factor among the NMR microcoils published previously. With our approach, the microcoil readily integrates with the sample chamber MRR measurements. Another unique feature of the adhesive-based technique is that the detachable sample chamber can be disposed of after each measurement without affecting the microcoil assembly. Therefore, the microcoil can be reused for multiple measurements. Unlike conventional microfabrication methods, there is no need for cleaning the sample chamber before every measurement and the cross-contamination issue between different samples is eliminated. The results obtained from the microcoil for the parametric study of the hematocrit–R2 relationship agree well with the data obtained with the conventional solenoid-type coil. In addition, the ability of the microcoil to detect a subtle change in the blood hematocrit level could open the door for the development of a portable MRR device to aid the diagnosis of anemia caused by a low number of red blood cells.

The details of this collaborative work between SMART, NTU and MIT is published now in the online issue of the journal "Lab on a Chip" (Tian Fook Kong (NTU/SMART), Weng Kung Peng (SMART), Trung Dung Luong (NTU), Nam-Trung Nguyen (NTU) and Jongyoon Han (MIT/SMART), "Adhesive-based liquid metal radio-frequency microcoil for magnetic resonance relaxometry measurement", Lab on a Chip, DOI: 10.1039/c1lc20853e)

(a) Schematic diagram of the stacking approach for the fabrication of a multilayer integrated NMR microcoil and the sample chamber. The microcoil consists of three layers: (i) the spiral channel; (ii) the interconnect; and (iii) the lead-out channel, while the sample chamber is placed directly on top of the assembled microcoil for MRR measurements. The required sample volume is 5 mL and can be disposed and replaced without affecting the microcoil. (b) The integrated patch of the liquid-metal microcoil and microfluidic chamber is attached to the bottom part of the NMR probe. The probe is placed inside a 0.5 T permanent magnet. (c) Schematic diagram for the assembled MRR device. The large contact areas between the PCB metal contact pads and liquid metal ensures low contact resistance between the microcoil and the external device (NMR probe). (d) A simple L-network for matching the microcoil impedance to 50 U and tuning the resonance frequency of the coil to 21.65 MHz for 0.5 T proton magnetic relaxometry measurements. Electrical signal passes through from the spiral coil to the bottom lead out channel through a middle interconnect layer. Misalignment between these three layers would cause an open circuit. The typical resistance of a planar microcoil with both width and gap of 250 mm is approximately 0.3 U.The probe is connected to a NMR spectrometer via a RF coaxial cable.