Abstract
This paper presents a novel, highly sensitive and ultra-small fluorescent detection system, including an autonomous capillary fluid manipulation chip. The optical detector integrates a LED light source, all necessary optical components, and a photodiode with preamplifier into one package of about 2 cm × 2 cm × 2 cm. Also, the low-cost and simple pumpless microfluidic device works well in sample preparation and manipulation. This chip consists of capillary stop valves and trigger valves which are fabricated by lithography and then bonded with a polydimethylsiloxane-ethylene oxide polymer polydimethylsiloxane (PEO-PDMS) cover. The contact angle of the PEO-PDMS can be adjusted by changing the concentration of the PEO. Hence, the fluidic chip can achieve functionalities such as timing features and basic logical functions. The prototype has been tested by fluorescence dye 5-Carboxyfluorescein (5-FAM) dissolved into the solvent DMSO (Dimethyl Sulfoxide). The results prove a remarkable sensitivity at a pico-scale molar, around 1.08 pM. The low-cost and miniaturized optical detection system, with a self-control capillary-driven microfluidic chip developed in this work, can be used as the crucial parts in portable biochemical detection applications and point of care testing.
Highlights
In the 1990s, microfluidic technologies and lab-on-a-chip were perceived as having potential to be powerful applications due to their advantages of their small size, low volume requirement for samples, and accurate analysis
The ordinary glass is usually much more hydrophilic so that the liquid may not stop at the opening of the stop valve, but it is good for liquid flowing fast in the capillary channel. Another cover sheet for the microchip is the widely used ordinary PDMS, which is very hydrophobic which makes the liquid flow slowly and even stop moving forward in the capillary channel sometimes. According to these existing difficulties of designing the effective capillary channel and stop valve, we propose a hydrophilic surface modified PDMS, which is used as the microchip cover and adjusts the contact angle of the PDMS to balance the fluid flowing in capillary channels as well as to be stable and stationary at the valve opening
To insure the high sensitivity, superbright light emitting diode (LED) and highly sensitive photodiode with integrated preamplifier are accepted as the light source and detection sensor
Summary
In the 1990s, microfluidic technologies and lab-on-a-chip were perceived as having potential to be powerful applications due to their advantages of their small size, low volume requirement for samples, and accurate analysis. Integrating fluid actuation, sample pre-treatment, sample separation, signal detection, and signal amplification into a single device have been highly developed [1]. Based on these technologies, currently many bio-detection systems are widely studied, such as the electrochemical method, refractive metrology, fluorescent detection, conductive detection, infrared detection, Raman detection, and mass spectrometry, which have been presented in other researchers’. The fluorescence detection uses a certain wavelength and high energy beam such as a laser or LED to excite unknown sample characters with a fluorescent label [3,4]. In order to achieve the high sensitivity, conventional bio-fluorescent systems usually adapt a charge-coupled device (CCD) camera, detection microscopy [7]
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