Wireless Microfluidic Sensor Based On Low Temperature Co-Fired Ceramic (LTCC) Technology

Microfluidics is the technology that manipulates small amount of liquids using channels with small dimension,which has been paid continual attention by academia and industry since its inception.Most of the current existing microfluidic devices and systems are based on the principles of optical and electrochemical detection.The complexity and high cost associated with the optical and electrochemical detection limit its large-scale application.Wireless microfluidic sensors have attracted much attention due to their inherent advantages of non-fluorescent labeling,non-intrusive detection and portability.Inductor-Capacitor?LC?sensors based on electromagnetic coupling principle facilitates the realization of wireless microfluidic sensor because they are flexible in designing,ease of fabricating and cost effective.On the other hand,low temperature co-fired ceramics?LTCC?are very suitable for the fabrication of LC wireless microfluidic sensors due to its high temperature resistance,corrosion resistance and most importantly,the ability to integrate complex three dimensional structures and electronic components.We propose a novel LC wireless microfluidic sensor based on LTCC technology in such background,the main contents are as follows.1?The structure of LC wireless microfluidic sensor has been designed basing on the equivalent circuit model of LC resonant antenna,theoretical calculation of effective permittivity and technical characteristics of LTCC.The electromagnetic-fluid coupling simulation is carried out to analyze the electromagnetic distribution of the designed sensor.The effective permittivity of mixed media is calculated through different formulas,and then the curve of calculated resonant frequency versus permittivity of liquid is obtained.LC wireless microfluidic sensor with initial resonant frequency 134.2MHz was fabricated through LTCC process.2?The signal response of the sensor to non-ionic solutions were tested.The measured results are in good agreement with the calculated results based on Maxwell-Garnett formula.And after introducing deionized water into the microfluidic sensor,the change of resonant frequency?1)/1)is⁴4%,which is the highest value compared with the relevant reported work.The sensor sensitively response to the aqueous ethanol and glucose solution with different concentrations.Regression analysis indicates that resonant frequency has a good quadratic fitting relationship with the weight fraction of ethanol and a good linear relationship with the mole fraction of glucose.The relation of S11 resonant frequency and amplitude to the dielectric properties of non-ionic solutions are determined.3?The signal response of the sensor to ionic solutions like aqueous NaCl,Na₂CO₃and sodium citrate solutions were tested.The amplitude of S11 was sensitive to the alteration in the concentration of salt solution,especially in low concentration.Taking NaCl as an example,the sensitivity of 1.0 dB/mM was obtained in the concentration range of 0 to 5 mM.A critical point appears in the curve of S11 amplitude versus concentration of salt solution.The critical concentration is verified to be related to the conductivity of the salt solution.Although the critical concentration varies with the types of salt solution,they have the same conductivity?⁰.37 S/m,20??.With the increase of salt solution concentration,the plate capacitance increase due to the increase of liquid conductivity,causing the decrease of resonant frequency.4?The signal response to different concentrations of glucose in 150 mM aqueous NaCl solution were tested.It was found that the resonant frequency was more sensitive to the variation of glucose concentration in salt solution than water solution.The sensitivity of the sensor was about 5.18 kHz/?mg/mL?at the concentration range of 0to 200 mg/mL,14.58 kHz/?mg/mL?at the concentration range of 240 to 400 mg/mL,both of which are higher than the corresponding sensitivity of 2.25 kHz/?mg/mL?in aqueous solution.This is due to the fact that the addition of glucose greatly reduces the conductivity of salt solution and consequently reduces the plate capacitance.5?The biocompatibility of borosilicate LTCC materials was studied.The results indicate that the excessive release of boron inhibit the proliferation of bone marrow mesenchymal stem cells?BMSC?,and the microporous structure on the surface of the materials promote the adhesion and proliferation of BMSC.The CABS possess the best biocompatibility to BMSC due to its good bio-stability and surface micro-pore structure and can be regarded as a potential candidate in the microfluidic biomedical devices.