A multi-functional electrochemical sensing system using microfluidic technology for the detection of urea and creatinine.

This study presents a new microfluidic system capable of precise measurements of two important biomarkers, urea and creatinine, automatically. In clinical applications, high levels of these two biomarkers are early indicators of nephropathy or renal failure and should be monitored on a regular basis. The microfluidic system is composed of a microfluidic chip, a control circuit system, a compressed air source and several electromagnetic valves to form a handheld system. The microfluidic chip is fabricated by using micro-electromechanical systems and microfluidic techniques comprising electrochemical sensor arrays and polydimethylsiloxane-based microfluidic structures such as micropumps/micromixers, normally closed valves and microchannels. The microfluidic system performs a variety of critical processes including sample pretreatment, mixing, transportation and detection on a single chip. The experimental results show that the entire procedure takes approximately 40 min, which is much faster than the traditional method (more than 6 h). Furthermore, the total sample volume consumed in each operation is only 0.1 mL, which is significantly less than that required in a large system (5 mL). The developed automatic microfluidic system may provide a powerful platform for further clinical applications.

An integrated microfluidic chip for non-immunological determination of urinary albumin.

This study presents an integrated microfluidic chip for non-immunologically determining the concentrations of albumin in clinical urine samples. This microchip integrates membrane-type micromixers and a fan-shaped micropump capable of simultaneously and precisely delivering assay reagents to react with 6 urine samples in one single operation. The experimental results show that the coefficient of variation in the pumping rate is 2.42%. More importantly, using this unique chip design, only 2 electromagnetic valves are required for the actuation of the micromixer and the micropump. The working range of the proposed microchip is 2-200 mg/L of albumin, which covers the range of interest for the determination of microalbuminuria. Moreover, statistical analysis show that the results obtained by the proposed microchip are in good agreement with the conventional detection method, based on immunological assays. This simple, inexpensive and microchip-based platform presents a promising alternative to conventional immunological assays for measurement of urinary albumin, and is well suited for clinical applications.

Integrated microfluidic system for rapid screening of CRP aptamers utilizing systematic evolution of ligands by exponential enrichment (SELEX).

The systematic evolution of ligands by exponential enrichment (SELEX) is an experimental procedure that allows screening of given molecular targets by desired binding affinities from an initial random pool of oligonucleotides and oligomers. The final products of SELEX are usually referred as aptamers, which are recognized as promising molecules for a variety of biomedical applications. However, SELEX is an iterative process requiring multiple rounds of extraction and amplification that demands significant time and labor. Therefore, this study presents a novel, automatic, miniature SELEX platform. As a demonstration, the rapid screening of C-reactive protein (CRP) aptamers was performed. By utilizing microfluidic technologies and magnetic beads conjugated with CRP, aptamers with a high affinity to CRP were extracted from a random single-strand deoxyribonucleic acid (ssDNA) pool. These aptamers were further amplified by an on-chip polymerase chain reaction (PCR) process. After five consecutive extraction and amplification cycles, a specific aptamer with the highest affinity was screened automatically. The screened aptamers were used as a recognition molecule for the detection of CRP. The developed microsystem demonstrated fast screening of CRP aptamers and can be used as a powerful tool to select analyte-specific aptamers for biomedical applications.