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Metal ions in high concentrations can pollute the marine environment. Human activities and industrial pollution are the causes of Cu2+ contamination. Here, we report our discovery of an enzyme method-based microfluidic that can be used to rapidly detect Cu2+ in seawater. In this method, Cu2+ is reduced to Cu+ to inhibit horseradish peroxidase (HRP) activity, which then results in the color distortion of the reaction solution. The chip provides both naked eye and spectrophotometer modalities. Cu2+ concentrations have an ideal linear relationship, with absorbance values ranging from 3.91 nM to 256 μM. The proposed enzyme method-based microfluidic chip detects Cu2+ with a limit of detection (LOD) of 0.87 nM. Other common metal ions do not affect the operation of the chip. The successful detection of Cu2+ was achieved using three real seawater samples, verifying the ability of the chip in practical applications. Furthermore, the chip realizes the functions of two AND gates in series and has potential practical implementations in biochemical detection and biological computing.

Background Early diagnosis and classification of infections increase the cure rate while decreasing complications, which is significant for severe infections, especially for war surgery. However, traditional methods rely on laborious operations and bulky devices. On the other hand, point-of-care (POC) methods suffer from limited robustness and accuracy. Therefore, it is of urgent demand to develop POC devices for rapid and accurate diagnosis of infections to fulfill on-site militarized requirements. Methods We developed a wave-shaped microfluidic chip (WMC) assisted multiplexed detection platform (WMC-MDP). WMC-MDP reduces detection time and improves repeatability through premixing of the samples and reaction of the reagents. We further combined the detection platform with the streptavidin–biotin (SA-B) amplified system to enhance the sensitivity while using chemiluminescence (CL) intensity as signal readout. We realized simultaneous detection of C-reactive protein (CRP), procalcitonin (PCT), and interleukin-6 (IL-6) on the detection platform and evaluated the sensitivity, linear range, selectivity, and repeatability. Finally, we finished detecting 15 samples from volunteers and compared the results with commercial ELISA kits. Results Detection of CRP, PCT, and IL-6 exhibited good linear relationships between CL intensities and concentrations in the range of 1.25–40 μg/ml, 0.4–12.8 ng/ml, and 50–1600 pg/ml, respectively. The limit of detection of CRP, PCT, and IL-6 were 0.54 μg/ml, 0.11 ng/ml, and 16.25 pg/ml, respectively. WMC-MDP is capable of good adequate selectivity and repeatability. The whole detection procedure takes only 22 min that meets the requirements of a POC device. Results of 15 samples from volunteers were consistent with the results detected by commercial ELISA kits. Conclusions WMC-MDP allows simultaneous, rapid, and sensitive detection of CRP, PCT, and IL-6 with satisfactory selectivity and repeatability, requiring minimal manipulation. However, WMC-MDP takes advantage of being a microfluidic device showing the coefficients of variation less than 10% enabling WMC-MDP to be a type of point-of-care testing (POCT). Therefore, WMC-MDP provides a promising alternative to POCT of multiple biomarkers. We believe the practical application of WMC-MDP in militarized fields will revolutionize infection diagnosis for soldiers.

Existing methods for detecting cardiac markers are difficult to be applied in point-of-care testing (POCT) due to complex operation, long time consumption, and low sensitivity. Here, we report a snail-shaped microfluidic chip (SMC) for the multiplex detection of cTnI, CK-MB, and Myo with high sensitivity and a short detection time. The SMC consists of a sandwich structure: a channel layer with a mixer and reaction zone, a reaction layer coated with capture antibodies, and a base layer. The opening or closing of the microchannels is realized by controlling the downward movement of the press-type mechanical valve. The chemiluminescence method was used as a signal readout, and the experimental conditions were optimized. SMC could detect cTnI, CK-MB, and Myo at concentrations as low as 1.02, 1.37, and 4.15. The SMC will be a promising platform for a simultaneous determination of multianalytes and shows a potential application in POCT.

Micromixers with the microchannel structure can enable rapid and efficient mixing of multiple types of fluids on a microfluidic chip. Herein, we report the mixing performance of three passive micromixers based on the different mathematical spiral structures. We study the fluid flow characteristics of Archimedes spiral, Fermat spiral, and hyperbolic spiral structures with various channel widths and Reynolds number (Re) ranging from 0 to 10 via numerical simulation and visualization experiments. In addition, we analyze the mechanism of streamlines and Dean vortices at different cross sections during fluid flows. As the fluid flows in the Fermat spiral channel, the centrifugal force induces the Dean vortex to form a chaotic advection, enhancing the fluid mixing performance. By integrating the Fermat spiral channel into a microfluidic chip, we successfully detect acute myocardial infarction (AMI) marker with the double-antibody sandwich method and reduce the detection time to 10 min. This method has a low reagent consumption and a high reaction efficiency and demonstrates great potential in point-of-care testing (POCT).