Capacitive microsystems for biological sensing

Electrical Chips for Biological Point-of-Care Detection

As the future of health care diagnostics moves toward more portable and personalized techniques, there is immense potential to harness the power of electrical signals for biological sensing and diagnostic applications at the point of care. Electrical biochips can be used to both manipulate and sense biological entities, as they can have several inherent advantages, including on-chip sample preparation, label-free detection, reduced cost and complexity, decreased sample volumes, increased portability, and large-scale multiplexing. The advantages of fully integrated electrical biochip platforms are particularly attractive for point-of-care systems. This review summarizes these electrical lab-on-a-chip technologies and highlights opportunities to accelerate the transition from academic publications to commercial success.

Paper-based rapid detection of pork and chicken using LAMP–magnetic bead aggregates

Magnetic beads (MBs) have been widely used for DNA quantification.

Printed and flexible biosensor for antioxidants using interdigitated ink-jetted electrodes and gravure-deposited active layer

Printing techniques have been extensively used in the fabrication of organic electronic devices, such as light-emitting diodes and display backplanes. These techniques, in particular inkjet printing, are being employed for the localized dispensing of solutions containing biological molecules and cells, leading to the fabrication of bio-functional microarrays and biosensors. Here, we report the fabrication of an all-printed and flexible biosensor for antioxidants. Gold (Au) interdigitated electrodes (IDEs) with sub-100 µm features were directly inkjet-printed on plastic substrates using a nanoparticle-based ink. Conductivities as high as 5×10(6) S/m (12% of bulk Au) were attained after sintering was conducted at plastic-compatible 200 °C for 6 h. The enzyme Tyrosinase (Tyr) was used in the active layer of the biosensors, being innovatively deposited by large-area rotogravure printing. A tailor-made ink was studied, and the residual activity of the enzyme was 85% after additives incorporation, and 15.5% after gravure printing. Au IDEs were coated with gravure films of the Tyr-containing ink, and the biosensor was encapsulated with a cellulose acetate dip-coating film to avoid dissolution. The biosensor impedance magnitude increases linearly with the concentration of a model antioxidant, allowing for the construction of a calibration curve. Control experiments demonstrated the molecular recognition characteristic inferred by the enzyme. We found that the biosensor sensitivity and the limit of detection were, respectively, 5.68 Ω/µm and 200 µM. In conclusion, a disposable, light-weight, all-printed and flexible biosensor for antioxidants was successfully fabricated using fast and large-area printing techniques. This opens the door for the fabrication of technological products using roll-to-roll processes.

Integrated biochip for label-free and real-time detection of DNA amplification by contactless impedance measurements based on interdigitated electrodes

Here, we introduce an integrated biochip which offers accurate thermal control and sensitive electrochemical detection of DNA amplification in real-time. The biochip includes a 10-μl microchamber, a temperature sensor, a heater, and a contactless impedance biosensor. A pair of interdigitated electrodes is employed as the impedance biosensor and the products of the amplification are determined directly through tracing the impedance change, without using any labels, redox indicators, or probes. Real-time monitoring of strand-displacement amplification and rolling circle amplification was successfully performed on the biochip and a detection limit of 1 nM was achieved. Amplification starting at an initial concentration of 10 nM could be discriminated from that starting at 1 nM started concentration as well as from the negative control. Since an insulation layer covers the electrodes, the electrodes are spared from erosion, hydrolysis and bubble formation on the surface, thus, ensuring a long lifetime and a high reusability of the sensor. In comparison to bench-top apparatus, our chip shows good efficiency, sensitivity, accuracy, and versatility. Our system requires only simple equipments and simple skills, and can easily be miniaturized into a micro-scale system. The system will then be suitable for a handheld portable device, which can be applied in remote areas. It covers merits such as low cost, low-power consumption, rapid response, real-time monitoring, label-free detection, and high-throughput detection.

Surface stress-based biosensors

Surface stress-based biosensors, as one kind of label-free biosensors, have attracted lots of attention in the process of information gathering and measurement for the biological, chemical and medical application with the development of technology and society. This kind of biosensors offers many advantages such as short response time (less than milliseconds) and a typical sensitivity at nanogram, picoliter, femtojoule and attomolar level. Furthermore, it simplifies sample preparation and testing procedures. In this work, progress made towards the use of surface stress-based biosensors for achieving better performance is critically reviewed, including our recent achievement, the optimally circular membrane-based biosensors and biosensor array. The further scientific and technological challenges in this field are also summarized. Critical remark and future steps towards the ultimate surface stress-based biosensors are addressed.

Discriminating DNA mismatches by electrochemical and gravimetric techniques

A silicon nitride functionalized electrode and a 104 MHz lithium tantalate (LiTaO₃) surface acoustic wave (SAW) sensor have been used to investigate target-probe recognition processes. Electrochemical and gravimetric measurements have been considered to monitor hybridization of single base mismatch (SBM) in synthetic oligonucleotides and single-nucleotide polymorphisms ApoE in real clinical genotypes. Obvious discrimination of SBM in nucleotides has been shown by both gravimetric and electrochemical techniques, without labeling nor amplification. Investigations on mismatches nature and position have also been considered. For guanine-adenine (GA), guanine-thymine (GT) and guanine-guanine (GG) mismatches, the sensors responses present a dependence upon positions. Considering the capacitance variations and hybridization rates, results showed that gravimetric transduction is more sensitive than electrochemical one. Moreover, the highest value of GT hybridization rate (in the middle position) was found in accordance with the nearest-neighbor model, where the considered configuration appears as the most thermodynamically stable. For the real samples, where the electrochemical transduction, by combining capacitance and flat-band potential measurements, were found more sensitive, the results show that the realized sensor permits an unambiguous discrimination of recognition between fully complementary, non-complementary and single base mismatched targets, and even between the combination of differently matched strands.

Impact of DNA sequence and oligonucleotide length on a polythiophene-based fluorescent DNA biosensor

DNA hybridization is a universal and specific mechanism for the recognition of biological targets. Some cationic polythiophene transducers sensitive to DNA structure have been previously utilized to detect such biomolecules. Further characterization of these systems indicates that both DNA sequence composition and length modulate the biosensor performance. It appears that different repeated sequence patterns cause different conformational changes of the polythiophene, from a more relaxed form to an extremely rigid one. A length difference between the DNA oligonucleotide probe and target has a detrimental effect on the fluorescent signal, but it can be attenuated by changing the sequence composition of the protruding target sequence. This demonstrates that the nature of DNA can be critical for hybridization-based detection systems.

Overview of micro- and nano-technology tools for stem cell applications: micropatterned and microelectronic devices

In the past few decades the scientific community has been recognizing the paramount role of the cell microenvironment in determining cell behavior. In parallel, the study of human stem cells for their potential therapeutic applications has been progressing constantly. The use of advanced technologies, enabling one to mimic the in vivo stem cell microenviroment and to study stem cell physiology and physio-pathology, in settings that better predict human cell biology, is becoming the object of much research effort. In this review we will detail the most relevant and recent advances in the field of biosensors and micro- and nano-technologies in general, highlighting advantages and disadvantages. Particular attention will be devoted to those applications employing stem cells as a sensing element.

Real-time monitoring of strand-displacement DNA amplification by a contactless electrochemical microsystem using interdigitated electrodes

This paper reports the design and implementation of a contactless conductivity detection system which combines a thermal control cell, a data processing system and an electrochemical (EC) cell for label-free isothermal nucleic acid amplification and real-time monitoring. The EC cell consists of a microchamber and interdigitated electrodes as the contactless conductivity biosensor with a cover slip as insulation. In our work, contactless EC measurements, the effects of trehalose on amplification, and chip surface treatment are investigated. With the superior performance of the biosensor, the device can detect the amount of pure DNA at concentrations less than 0.1 pg μl(-1). The EC cell, integrated with a heater and a temperature sensor, has successfully implemented nicking-based strand-displacement amplification at an initial concentration of 2.5 μM and the yields are monitored directly (dismissing the use of probes or labels) on-line. This contactless detector carries important advantages: high anti-interference capability, long detector life, high reusability and low cost. In addition, the small size, low power consumption and portability of the detection cell give the system the potential to be highly integrated for use in field service and point of care applications.

Biocompatibility of CS-PPy nanocomposites and their application to glucose biosensor

The intrinsic properties and application potential of nanocolloids are mainly determined by size, shape, composition, and structure. In this case, a novel glucose biosensor was developed by using the chitosan-polypyrrole (CS-PPy) nanocomposites as special modified materials that coating onto the surface of glassy carbon electrode (GCE). The CS-PPy nanocomposites were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Moreover, the interaction of CS-PPy nanocomposites with glucose oxidase (GOD) was also investigated by the combined studies with Fourier transform infrared spectroscopy (FTIR) and circular dichroism spectroscopy (CD). Due to the conductivity of polypyrrole (PPy), good biocompatibility of CS, and advantages of nanoparticles, CS-PPy nanocomposites were chosen and designed to modify the GCE for the retention of GOD's biological activity and the vantage of electron transfer between GOD and electrodes. The GOD biosensor exhibited a fast amperometric response (5s) to glucose, a good linear current-time relation over a wide range of glucose concentrations from 5.00×10(-4) to 1.47×10(-1)M, and a low detection limit of 1.55×10(-5)M. The GOD biosensor modified with CS-PPy nanocomposites will have essential meaning and practical application in future that attributed to the simple method of fabrication and good performance.

A personalized life: biomarker monitoring from cradle to grave

Considering the holy grail of future medical treatment being personalized medicines, biomarker research will become more and more the focus for attention not only to develop new medical treatment regimes, based on changes in biomarker patterns, but also for nutritional advice to guarantee a lifelong optimized health condition. The current review gives an outline of how personalized medicine can become established for actual medical treatment using new biomarker concepts. Starting from the development of biomarker research using mainly immunological techniques, the review gives an overview about biomarkers of prediction evolved and focuses on new methodology for the identification of biomarkers using hyphenated analytical techniques like metabolomics and lipidomics. The actual use of multivariate statistical methods in combination with metabolomics and lipidomics is discussed not only for medical treatment but also for precautionary risk identification in human biomonitoring studies.