Investigation of process-affected zone in ultrasonic embossing of microchannels on thermoplastic substrates

In this paper, the process-affected zone in ultrasonically embossed thermoplastic substrates is investigated both numerically and experimentally. Commercialization of microfluidic devices challenges the need for high-speed manufacturing of plastic chips. Ultrasonic embossing is considered as an alternative method since the cycle time can be as low as a few seconds per chip while keeping the cost relatively low. To examine the ultrasonic embossing process, experiments were carried out to replicate 200 mu m wide and 150 mu m high straight channels on 3 mm thick polymethylmethacrylate (PMMA) substrates. The mold was fabricated by milling on aluminum. The features could be embossed by applying an 85 N static force at 28 kHz ultrasonic vibration and 10 mu m amplitude for 5 s at room temperature with replication rates of 99.5 % and 100 % for the width and the depth, respectively. During the experiments, a clearly visible process-affected zone typically bounded by a half-circle with the center at the channel axis was observed. It was proven that the process-affected zone was bounded by the isothermal surface at the glass transition temperature of the substrate material (107 degrees C), both numerically and experimentally. It was also shown that the composition of the substrate material remains unaffected within the process-affected zone

A capillary driven microfluidic chip for SERS based hCG detection

In this study, a capillary driven microfluidic chip-based immunoassay was developed for the determination of Human Chorionic Gonadotropin (hCG) protein, which is prohibited by the World Anti-Doping Agency (WADA). Here, we used antibody modified magnetic metal organic framework nanoparticles (MMOFs) as a capture prob in urine sample. MMOF captured hCG was transferred in a capillary driven microfluidic chip consisting of four chambers, and the interaction of MMOF with gold nanorods labelled with 5,5'-Dithiobis-(2-nitrobenzoic acid) (DTNB) as a Raman label was carried out in the capillary driven microfluidic chip. The movement of MMOF through first chamber to the last chamber was achieved with a simple magnet. In the last chamber of capillary driven microfluidic chip, SERS signals of DTNB molecules from the sandwich complex were recorded using a Raman spectrophotometer. The selectivity of the developed method was demonstrated by applying the same procedure for the detection of Human Luteinizing Hormone (hLH), Human Chorionic Gonadotropin Hormone (hGH) and Immunoglobulin G (IgG) protein. The regression coefficient and limit of detection obtained from the standard addition method were found as 0,9985 and 0,61 IU/L, respectively. Furthermore, the conventional ELISA method confirmed that the results obtained by the presented method were acceptable with the similarity of 97.9% in terms of average recovery value, for the detection of hCG in urine samples. The analysis system developed for target proteins will be an alternative technique such as Western Blot used in routine analysis that is expensive and time consuming

Multiplex enumeration ofEscherichia coliandSalmonella enteritidisin a passive capillary microfluidic chip

Multiplex detection and quantification of bacteria in water by using portable devices are particularly essential in low and middle-income countries where access to clean drinking water is limited. Addressing this crucial problem, we report a highly sensitive immunoassay sensor system utilizing the fluorescence technique with magnetic nanoparticles (MNPs) to separate target bacteria and two different types of quantum dots (CdTe and Ni doped CdTe QDs) incorporated into a passive microfluidic chip to transport and to form sandwich complexes for the detection of two target bacteria, namelyEscherichia coli(E. coli) andSalmonella enteritidis(S. enteritidis) in less than 60 min. The assay is carried out on a capillary driven microfluidic chip that can be operated by merely pipetting the samples and reagents, and fluorescence measurements are done by using a handheld fluorescence spectrophotometer, which renders the system portable. The linear range of the method was found to be 10(1)to 10(5)cfu mL(-1)for bothE. coliandS. enteritidis. The limit of detection (LOD) was calculated to be 5 and 3 cfu mL(-1)forE. coliandS. enteritidis, respectively. The selectivity of the method was examined by testingEnterobacter dissolvens(E. dissolvens) andStaphylococcus aureus(S. aureus) samples, and no significant interference was observed. The method was also demonstrated to detect bacteria in tap water and lake water samples spiked with target bacteria