Development of a package-free transparent disposable biosensor chip for simultaneous measurements of blood constituents and investigation of its storage stability

Current status of water environment and their microbial biosensor techniques - Part II: Recent trends in microbial biosensor development

In Part I of the present review series, I presented the current state of the water environment by focusing on Japanese cases and discussed the need to further develop microbial biosensor technologies for the actual water environment. I comprehensively present trends after approximately 2010 in microbial biosensor development for the water environment. In the first section, after briefly summarizing historical studies, recent studies on microbial biosensor principles are introduced. In the second section, recent application studies for the water environment are also introduced. Finally, I conclude the present review series by describing the need to further develop microbial biosensor technologies. Graphical abstract Current water pollution indirectly occurs by anthropogenic eutrophication (Part I). Recent trends in microbial biosensor development for water environment are described in part II of the present review series.

Avoiding Resistance Limitations in High-Performance Transparent Supercapacitor Electrodes Based on Large-Area, High-Conductivity PEDOT:PSS Films

This work describes the potential of thin, spray-deposited, large-area poly(3,4-ethylenedioxythiophene)/poly(styrene-4-sulfonate) (

PEDOT

PSS) conducting polymer films for use as transparent supercapacitor electrodes. To facilitate this, we provide a detailed explanation of the factors limiting the performance of such electrodes. These films have a very low optical conductivity of σop = 24 S/cm (at 550 nm), crucial for this application, and a reasonable volumetric capacitance of CV = 41 F/cm(3). Secondary doping with formic acid gives these films a DC conductivity of σDC = 936 S/cm, allowing them to perform both as a transparent conductor/current collector and transparent supercapacitor electrode. Small-area films (A ∼ 1 cm(2)) display measured areal capacitance as high as 1 mF/cm(2), even for reasonably transparent electrodes (T ∼ 80%). However, in real devices, the absolute capacitance will be maximized by increasing the device area. As such, here, we measure the electrode performance as a function of its length and width. We find that the measured areal capacitance falls dramatically with scan rate and sample length but is independent of width. We show that this is because the measured areal capacitance is limited by the electrical resistance of the electrode. We have derived an equation for the measured areal capacitance as a function of scan rate and electrode lateral dimensions that fits the data extremely well up to scan rates of ∼1000 mV/s (corresponding to charge/discharge times > 0.6 s). These results are self-consistent with independent analysis of the electrical and impedance properties of the electrodes. These results can be used to find limiting combinations of electrode length and scan rate, beyond which electrode performance falls dramatically. We use these insights to build large-area (∼100 cm(2)) supercapacitors using electrodes that are 95% transparent, providing a capacitance of ∼12 mF (at 50 mV/s), significantly higher than that of any previously reported transparent supercapacitor.

Disposable electrochemiluminescent biosensor using bidentate-chelated CdTe quantum dots as emitters for sensitive detection of glucose

A novel disposable solid-state electrochemiluminescent (ECL) biosensor was fabricated by immobilizing glucose oxidase and surface-unpassivated CdTe quantum dots (QDs) on a screen-printed carbon electrode (SPCE). The surface morphology of the biosensor was characterized with scanning electron microscopy and atomic force microscopy. With dissolved O(2) as an endogenous coreactant, QDs/SPCE showed strong ECL emission in pH 9.0 HCl-Tris buffer solution with low ECL peak potential at -0.89 V. The ECL intensity was twice that with hydrogen peroxide as coreactant at the same concentration. This phenomenon meant the ECL decreased upon consumption of dissolved O(2) and thus could be applied to the construction of oxidase-based ECL biosensors. With glucose oxidase as a model enzyme, the biosensor showed rapid response to glucose with a linear range of 0.8 to 100 μM and a detection limit of 0.3 μM. Further detection of glucose contained in human serum samples showed acceptable sensitivity and selectivity. This work provided a promising application of QDs in ECL-based disposable biosensors.

Continuous-flow multi-analyte biosensor cartridge with controllable linear response range

This article presents the design and fabrication of a microfluidic biosensor cartridge for the continuous and simultaneous measurement of biologically relevant analytes in a sample solution. The biosensor principle is based on the amperometric detection of hydrogen peroxide using enzyme-modified electrodes. The low-integrated and disposable cartridge is fabricated in PDMS and SU-8 by rapid prototyping. The device is designed in such a way that it addresses two major challenges of biosensors using microfluidics approaches. Firstly, the enzymatic membrane is deposited on top of the platinum electrodes via a microfluidic deposition channel from outside the cartridge. This decouples the membrane deposition from the cartridge fabrication and enables the user to decide when and with what mixture he wants to modify the electrode. Secondly, by using laminar sheath-flow of the sample and a buffer solution, a dynamic diffusion layer is created. The analyte has to diffuse through the buffer solution layer before it can reach the immobilized enzyme membrane on the electrode. Controlling of the thickness of the diffusion layer by variation of the flow-rate of the two layers enables the user to adjust the sensitivity and the linear region of the sensor. The point where the buffer and sample stream join proved critical in creating the laminar sheath-flow. Results of computational simulations considering fluid dynamics and diffusion are presented. The consistency of the device was investigated through detection of glucose and lactate and are in accordance with the CFD simulations. A sensitivity of 157+/-28 nA/mM for the glucose sensor and 79+/-12 nA/mM for the lactate sensor was obtained. The linear response range of these biosensors could be increased from initially 2 mM up to 15 mM with a limit of detection of 0.2 mM.