http://www.mdpi.com/journal/biosensors Latest open access articles published in Biosensors at http://www.mdpi.com/journal/biosensors http://www.mdpi.com/2079-6374/2/2/205 The detection of myoglobin (Myo), cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and b-type natriuretic peptide (BNP) plays a vital role in diagnosing cardiovascular diseases. Here we present single site-specific polyaniline (PANI) nanowire biosensors that can detect cardiac biomarkers such as Myo, cTnI, CK-MB, and BNP with ultra-high sensitivity and good specificity. Using single PANI nanowire-based biosensors integrated with microfluidic channels, very low concentrations of Myo (100 pg/mL), cTnI (250 fg/mL), CK-MB (150 fg/mL), and BNP (50 fg/mL) were detected. The single PANI nanowire-based biosensors displayed linear sensing profiles for concentrations ranging from hundreds (fg/mL) to tens (ng/mL). In addition, devices showed a fast (few minutes) response satisfying respective reference conditions for Myo, cTnI, CK-MB, and BNP diagnosis of heart failure and for determining the stage of the disease. This single PANI nanowire-based biosensor demonstrated superior biosensing reliability with the feasibility of label free detection and improved processing cost efficiency due to good biocompatibility of PANI to monoclonal antibodies (mAbs). Therefore, this development of single PANI nanowire-based biosensors can be applied to other biosensors for cancer or other diseases. http://www.mdpi.com/2079-6374/2/2/205 Mon, 14 May 2012 00:00:00 CEST Biosensors 2012-05-14 2 2 Article 205 220 2079-6374 Detection of Cardiac Biomarkers Using Single Polyaniline Nanowire-Based Conductometric Biosensors 2012-05-14 doi: 10.3390/bios2020205 Innam Lee Xiliang Luo Jiyong Huang Xinyan Tracy Cui Minhee Yun http://www.mdpi.com/2079-6374/2/2/189 In view of the role ascribed to the peroxidatic activity of degradation products of cytochrome c (cyt c) in the processes of apoptosis, we investigate the catalytic potential of heme and of the cyt c derived heme peptide MP-11 to catalyse the cathodic reduction of hydrogen peroxide and to oxidize aromatic compounds. In order to check whether cyt c has an enzymatic activity in the native state where the protein matrix should suppress the inherent peroxidatic activity of its heme prosthetic group, we applied a biocompatible immobilization matrix and very low concentrations of the co-substrate H2O2. The biocatalysts were entrapped on the surface of a glassy carbon electrode in a biocompatible chitosan layer which contained gold nanoparticles. The electrochemical signal for the peroxide reduction is generated by the redox conversion of the heme group, whilst a reaction product of the substrate oxidation is cathodically reduced in the substrate indication. The catalytic efficiency of microperoxidase-11 is sufficient for sensors indicating HRP substrates, e.g., p-aminophenol, paracetamol and catechol, but also the hydroxylation of aniline and dehalogenation of 4-fluoroaniline. The lower limit of detection for p-aminophenol is comparable to previously published papers with different enzyme systems. The peroxidatic activity of cyt c immobilized in the chitosan layer for catechol was found to be below 1 per mill and for p-aminophenol about 3% as compared with that of heme or MP-11. http://www.mdpi.com/2079-6374/2/2/189 Mon, 14 May 2012 00:00:00 CEST Biosensors 2012-05-14 2 2 Article 189 204 2079-6374 Peroxide-Dependent Analyte Conversion by the Heme Prosthetic Group, the Heme Peptide “Microperoxidase-11” and Cytochrome c on Chitosan Capped Gold Nanoparticles Modified Electrodes 2012-05-14 doi: 10.3390/bios2020189 Aysu Yarman Bettina Neumann Maria Bosserdt Nenad Gajovic-Eichelmann Frieder W. Scheller http://www.mdpi.com/2079-6374/2/2/171 Infection control is a key aspect of wound management strategies. Infection results in chemical imbalances and inflammation in the wound and may lead to prolonged healing times and degradation of the wound surface. Frequent changing of wound dressings may result in damage to healing tissues and an increased risk of infection. This paper presents the first results from a monitoring system that is being developed to detect presence and growth of bacteria in real time. It is based on impedance sensors that could be placed at the wound-dressing interface and potentially monitor bacterial growth in real time. As wounds can produce large volumes of exudate, the initial system reported here was developed to test for the presence of bacteria in suspension. Impedance was measured using disposable silver-silver chloride electrodes. The bacteria Staphylococcus aureus were chosen for the study as a species commonly isolated from wounds. The growth of bacteria was confirmed by plate counting methods and the impedance data were analysed for discernible differences in the impedance profiles to distinguish the absence and/or presence of bacteria. The main findings were that the impedance profiles obtained by silver-silver chloride sensors in bacterial suspensions could detect the presence of high cell densities. However, the presence of the silver-silver chloride electrodes tended to inhibit the growth of bacteria. These results indicate that there is potential to create a real time infection monitor for wounds based upon impedance sensing. http://www.mdpi.com/2079-6374/2/2/171 Wed, 09 May 2012 00:00:00 CEST Biosensors 2012-05-09 2 2 Article 171 188 2079-6374 Developing a Real Time Sensing System to Monitor Bacteria in Wound Dressings 2012-05-09 doi: 10.3390/bios2020171 Malcolm J. Farrow Iain S. Hunter Patricia Connolly http://www.mdpi.com/2079-6374/2/2/127 Cellular biochemical parameters can be used to reveal the physiological and functional information of various cells. Due to demonstrated high accuracy and non-invasiveness, electrochemical detection methods have been used for cell-based investigation. When combined with improved biosensor design and advanced measurement systems, the on-line biochemical analysis of living cells in vitro has been applied for biological mechanism study, drug screening and even environmental monitoring. In recent decades, new types of miniaturized electrochemical biosensor are emerging with the development of microfabrication technology. This review aims to give an overview of the microfabricated electrochemical cell-based biosensors, such as microelectrode arrays (MEA), the electric cell-substrate impedance sensing (ECIS) technique, and the light addressable potentiometric sensor (LAPS). The details in their working principles, measurement systems, and applications in cell monitoring are covered. Driven by the need for high throughput and multi-parameter detection proposed by biomedicine, the development trends of electrochemical cell-based biosensors are also introduced, including newly developed integrated biosensors, and the application of nanotechnology and microfluidic technology. http://www.mdpi.com/2079-6374/2/2/127 Wed, 25 Apr 2012 00:00:00 CEST Biosensors 2012-04-25 2 2 Review 127 170 2079-6374 Microfabricated Electrochemical Cell-Based Biosensors for Analysis of Living Cells In Vitro 2012-04-25 doi: 10.3390/bios2020127 Jun Wang Chengxiong Wu Ning Hu Jie Zhou Liping Du Ping Wang http://www.mdpi.com/2079-6374/2/2/114 New silicon nitride coated optical gratings were tested by means of Optical Waveguide Lightmode Spectroscopy (OWLS). A thin layer of 10 nm of transparent silicon nitride was deposited on commercial optical gratings by means of sputtering. The quality of the layer was tested by x-ray photoelectron spectroscopy and atomic force microscopy. As a proof of concept, the sensors were successfully tested with OWLS by monitoring the concentration dependence on the detection of an antibody-protein pair. The potential of the Si3N4 as functional layer in a real-time biosensor opens new ways for the integration of optical waveguides with microelectronics. http://www.mdpi.com/2079-6374/2/2/114 Tue, 10 Apr 2012 00:00:00 CEST Biosensors 2012-04-10 2 2 Article 114 126 2079-6374 Optical Gratings Coated with Thin Si3N4 Layer for Efficient Immunosensing by Optical Waveguide Lightmode Spectroscopy 2012-04-10 doi: 10.3390/bios2020114 Lorena Diéguez David Caballero Josep Calderer Mauricio Moreno Elena Martínez Josep Samitier http://www.mdpi.com/2079-6374/2/1/101 In this article we investigate the possibility of scaling down enzyme-gelatin modified electrodes by spin coating the enzyme-gelatin layer. Special attention is given to the electrochemical behavior of the selected enzymes inside the gelatin matrix. A glassy carbon electrode was used as a substrate to immobilize, in the first instance, horse heart cytochrome c (HHC) in a gelatin matrix. Both a drop dried and a spin coated layer was prepared. On scaling down, a transition from diffusion controlled reactions towards adsorption controlled reactions is observed. Compared to a drop dried electrode, a spin coated electrode showed a more stable electrochemical behavior. Next to HHC, we also incorporated catalase in a spin coated gelatin matrix immobilized on a glassy carbon electrode. By spincoating, highly uniform sub micrometer layers of biocompatible matrices can be constructed. A full electrochemical study and characterization of the modified surfaces has been carried out. It was clear that in the case of catalase, gluteraldehyde addition was needed to prevent leaking of the catalase from the gelatin matrix. http://www.mdpi.com/2079-6374/2/1/101 Thu, 15 Mar 2012 00:00:00 CET Biosensors 2012-03-15 2 1 Article 101 113 2079-6374 Enzyme-Gelatin Electrochemical Biosensors: Scaling Down 2012-03-15 doi: 10.3390/bios2010101 Karolien De Wael Stijn De Belder Sanaz Pilehvar Geert Van Steenberge Wouter Herrebout Hendrik A. Heering http://www.mdpi.com/2079-6374/2/1/83 The discovery over the past two decades of viable microbial communities within glaciers has promoted interest in the role of glaciers and ice sheets (the cryosphere) as contributors to subglacial erosion, global biodiversity, and in regulating global biogeochemical cycles. In situ or in-field detection and characterisation of microbial communities is becoming recognised as an important approach to improve our understanding of such communities. Within this context we demonstrate, for the first time, the ability to detect Gram-negative bacteria in glacial field-environments (including subglacial environments) via the detection of lipopolysaccharide (LPS); an important component of Gram-negative bacterial cell walls. In-field measurements were performed using the recently commercialised PyroGene® recombinant Factor C (rFC) endotoxin detection system and used in conjunction with a handheld fluorometer to measure the fluorescent endpoint of the assay. Twenty-seven glacial samples were collected from the surface, bed and terminus of a low-biomass Arctic valley glacier (Engabreen, Northern Norway), and were analysed in a field laboratory using the rFC assay. Sixteen of these samples returned positive LPS detection. This work demonstrates that LPS detection via rFC assay is a viable in-field method and is expected to be a useful proxy for microbial cell concentrations in low biomass environments. http://www.mdpi.com/2079-6374/2/1/83 Fri, 09 Mar 2012 00:00:00 CET Biosensors 2012-03-09 2 1 Article 83 100 2079-6374 In-Field Implementation of a Recombinant Factor C Assay for the Detection of Lipopolysaccharide as a Biomarker of Extant Life within Glacial Environments 2012-03-09 doi: 10.3390/bios2010083 Megan J. Barnett Jemma L. Wadham Miriam Jackson David C. Cullen http://www.mdpi.com/2079-6374/2/1/70 The focus of this paper is the development and investigation of properties of new nanostructured architecture for biosensors applications. Highly porous nanocomposite fibers were developed for use as active materials in biosensors. The nanocomposites comprised poly(lactic acid)(PLA)/multi-walled carbon nanotube (MWCNT) fibers obtained via solution-blow spinning onto indium tin oxide (ITO) electrodes. The electrocatalytic properties of nanocomposite-modified ITO electrodes were investigated toward hydrogen peroxide (H2O2) detection. We investigated the effect of carbon nanotube concentration and the time deposition of fibers on the sensors properties, viz., sensitivity and limit of detection. Cyclic voltammetry experiments revealed that the nanocomposite-modified electrodes displayed enhanced activity in the electrochemical reduction of H2O2, which offers a number of attractive features to be explored in development of an amperometric biosensor. Glucose oxidase (GOD) was further immobilized by drop coating on an optimized ITO electrode covered by poly(lactic acid)/carbon nanotube nanofibrous mats. The optimum biosensor response was linear up to 800 mM of glucose with a sensitivity of 358 nA·mM−1 and a Michaelis-Menten constant (KM) of 4.3 mM. These results demonstrate that the solution blow spun nanocomposite fibers have great potential for application as amperometric biosensors due to their high surface to volume ratio, high porosity and permeability of the substrate. The latter features may significantly enhance the field of glucose biosensors. http://www.mdpi.com/2079-6374/2/1/70 Mon, 27 Feb 2012 00:00:00 CET Biosensors 2012-02-27 2 1 Article 70 82 2079-6374 Poly(lactic acid)/Carbon Nanotube Fibers as Novel Platforms for Glucose Biosensors 2012-02-27 doi: 10.3390/bios2010070 Juliano Elvis Oliveira Luiz Henrique Capparelli Mattoso Eliton Souto Medeiros Valtencir Zucolotto http://www.mdpi.com/2079-6374/2/1/57 This paper describes the functionalization of magnetoelastic (ME) materials with Parylene-C coating to improve the surface reactivity to cellular response. Previous study has demonstrated that vibrating ME materials were capable of modulating cellular adhesion when activated by an externally applied AC magnetic field. However, since ME materials are not inherently biocompatible, surface modifications are needed for their implementation in biological settings. Here, the long-term stability of the ME material in an aqueous and biological environment is achieved by chemical-vapor deposition of a conformal Parylene-C layer, and further functionalized by methods of oxygen plasma etching and protein adsorption. In vitro cytotoxicity measurement and characterization of the vibrational behavior of the ME materials showed that Parylene-C coatings of 10 µm or greater could prevent hydrolytic degradation without sacrificing the vibrational behavior of the ME material. This work allows for long-term durability and functionality of ME materials in an aqueous and biological environment and makes the potential use of this technology in monitoring and modulating cellular behavior at the surface of implantable devices feasible. http://www.mdpi.com/2079-6374/2/1/57 Mon, 13 Feb 2012 00:00:00 CET Biosensors 2012-02-13 2 1 Article 57 69 2079-6374 Fabrication of Biocompatible, Vibrational Magnetoelastic Materials for Controlling Cellular Adhesion 2012-02-13 doi: 10.3390/bios2010057 Hal R. Holmes Ee Lim Tan Keat Ghee Ong Rupak M. Rajachar http://www.mdpi.com/2079-6374/2/1/43 Single domain antibodies (sdAb) are the recombinantly expressed variable regions from the heavy-chain-only antibodies found in camelids and sharks. SdAb are able to bind antigens with high affinity, and most are capable of refolding after heat or chemical denaturation to bind antigen again. Starting with our previously isolated ricin binding sdAb determined to bind to four non-overlapping epitopes, we constructed a series of sdAb pairs, which were genetically linked through peptides of different length. We designed the series so that the sdAb are linked in both orientations with respect to the joining peptide. We confirmed that each of the sdAb in the constructs was able to bind to the ricin target, and have evidence that they are both binding ricin simultaneously. Through this work we determined that the order of genetically linked sdAb seems more important than the linker length. The genetically linked sdAb allowed for improved ricin detection with better limits of detection than the best anti-ricin monoclonal we evaluated, however they were not able to refold as well as unlinked component sdAb. http://www.mdpi.com/2079-6374/2/1/43 Wed, 01 Feb 2012 00:00:00 CET Biosensors 2012-02-01 2 1 Article 43 56 2079-6374 Linking Single Domain Antibodies that Recognize Different Epitopes on the Same Target 2012-02-01 doi: 10.3390/bios2010043 Richard H. Glaven George P. Anderson Dan Zabetakis Jinny L. Liu Nina C. Long Ellen R. Goldman http://www.mdpi.com/2079-6374/2/1/32 Rapid, sensitive detection methods are of utmost importance for the identification of pathogens related to health and safety. Herein we report the development of a nucleic acid sequence-based lateral flow assay which achieves a low limit of detection using chemiluminescence. On-membrane enzymatic signal amplification is used to reduce the limit of detection to the sub-femtomol level. To demonstrate this assay, we detected synthetic nucleic acid sequences representative of Trypanosoma mRNA, the causative agent for African sleeping sickness, with relevance in human and animal health in sub-Saharan Africa. The intensity of the chemiluminescent signal was evaluated by using a charge-coupled device as well as a microtiter plate reader. We demonstrated that our lateral flow chemiluminescent assay has a very low limit of detection and is easy to use. The limit of detection was determined to be 0.5 fmols of nucleic acid target. http://www.mdpi.com/2079-6374/2/1/32 Wed, 18 Jan 2012 00:00:00 CET Biosensors 2012-01-18 2 1 Article 32 42 2079-6374 Development of Chemiluminescent Lateral Flow Assay for the Detection of Nucleic Acids 2012-01-18 doi: 10.3390/bios2010032 Yuhong Wang Catherine Fill Sam R. Nugen http://www.mdpi.com/2079-6374/2/1/15 Biological defense and security applications demand rapid, sensitive detection of bacterial pathogens. This work presents a novel qualitative electrochemical detection technique which is applied to two representative bacterial pathogens, Bacillus cereus (as a surrogate for B. anthracis) and Escherichia coli O157:H7, resulting in detection limits of 40 CFU/mL and 6 CFU/mL, respectively, from pure culture. Cyclic voltammetry is combined with immunomagnetic separation in a rapid method requiring approximately 1 h for presumptive positive/negative results. An immunofunctionalized magnetic/polyaniline core/shell nano-particle (c/sNP) is employed to extract target cells from the sample solution and magnetically position them on a screen-printed carbon electrode (SPCE) sensor. The presence of target cells significantly inhibits current flow between the electrically active c/sNPs and SPCE. This method has the potential to be adapted for a wide variety of target organisms and sample matrices, and to become a fully portable system for routine monitoring or emergency detection of bacterial pathogens. http://www.mdpi.com/2079-6374/2/1/15 Tue, 17 Jan 2012 00:00:00 CET Biosensors 2012-01-17 2 1 Article 15 31 2079-6374 Electrochemical Biosensor for Rapid and Sensitive Detection of Magnetically Extracted Bacterial Pathogens 2012-01-17 doi: 10.3390/bios2010015 Emma B. Setterington Evangelyn C. Alocilja http://www.mdpi.com/2079-6374/2/1/1 Electrochemical aptasensors, which are based on the specificity of aptamer-target recognition, with electrochemical transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. Aptamers are functional nucleic acids with specific and high affinity to their targets, similar to antibodies. However, they are completely selected in vitro in contrast to antibodies. Due to their stability, easy chemical modifications and proneness to nanostructured device construction, aptamer-based sensors have been incorporated in a variety of applications including electrochemical sensing devices. In recent years, the performance of aptasensors has been augmented by incorporating novel nanomaterials in the preparation of better electrochemical sensors. In this review, we summarize the recent trends in the use of nanomaterials for developing electrochemical aptasensors. http://www.mdpi.com/2079-6374/2/1/1 Fri, 13 Jan 2012 00:00:00 CET Biosensors 2012-01-13 2 1 Review 1 14 2079-6374 Graphene and Other Nanomaterial-Based Electrochemical Aptasensors 2012-01-13 doi: 10.3390/bios2010001 Frank J. Hernandez Veli Cengiz Ozalp http://www.mdpi.com/2079-6374/1/4/164 Film bulk acoustic resonators (FBAR) are mass sensitive, label-free biosensors that allow monitoring of the interaction between biomolecules. In this paper we use the FBAR to measure the binding of calcium and the CaMKII peptide to calmodulin. Because the mass of the calcium is too small to be detected, the conformational change caused by the binding process is measured by monitoring the resonant frequency and the motional resistance of the FBAR. The resonant frequency is a measure for the amount of mass coupled to the sensor while the motional resistance is influenced by the viscoelastic properties of the adsorbent. The measured frequency shift during the calcium adsorptions was found to be strongly dependent on the surface concentration of the immobilized calmodulin, which indicates that the measured signal is significantly influenced by the amount of water inside the calmodulin layer. By plotting the measured motional resistance against the frequency shift, a mass adsorption can be distinguished from processes involving measurable conformational changes. With this method three serial processes were identified during the peptide binding. The results show that the FBAR is a promising technology for the label-free measurement of conformational changes. http://www.mdpi.com/2079-6374/1/4/164 Wed, 14 Dec 2011 00:00:00 CET Biosensors 2011-12-14 1 4 Article 164 176 2079-6374 Conformational Changes of Calmodulin on Calcium and Peptide Binding Monitored by Film Bulk Acoustic Resonators 2011-12-14 doi: 10.3390/bios1040164 Martin Nirschl Johannes Ottl Janos Vörös http://www.mdpi.com/2079-6374/1/4/153 In this study, we have successfully demonstrated the fabrication of a biosensor based on well aligned single-crystal zinc oxide (ZnO) nanorods which were grown on gold coated glass substrate using a low temperature aqueous chemical growth (ACG) method. The ZnO nanorods were immobilized with penicillinase enzyme using the physical adsorption approach in combination with N-5-azido-2-nitrobenzoyloxysuccinimide (ANB-NOS) as cross linking molecules. The potentiometric response of the sensor configuration revealed good linearity over a large logarithmic concentration range from 100 µM to 100 mM. During the investigations, the proposed sensor showed a good stability with high sensitivity of ~121 mV/decade for sensing of penicillin. A quick electrochemical response of less than 5 s with a good selectivity, repeatability, reproducibility and a negligible response to common interferents such as Na1+, K1+, d-glucose, l-glucose, ascorbic acid, uric acid, urea, sucrose, lactose, glycine, penicilloic acid and cephalosporins, was observed. http://www.mdpi.com/2079-6374/1/4/153 Thu, 27 Oct 2011 00:00:00 CEST Biosensors 2011-10-27 1 4 Article 153 163 2079-6374 ZnO Nanorods Based Enzymatic Biosensor for Selective Determination of Penicillin 2011-10-27 doi: 10.3390/bios1040153 Zafar Hussain Ibupoto Syed Muhammad Usman Ali Kimleang Khun Chan Oeurn Chey Omer Nur Magnus Willander http://www.mdpi.com/2079-6374/1/4/134 A passive and wireless sensor was developed for monitoring pressure in vivo. Structurally, the pressure sensor, referred to as the magneto-harmonic pressure sensor, is an airtight chamber sealed with an elastic pressure membrane. A strip of magnetically-soft material is attached to the bottom of the chamber and a permanent magnet strip is embedded inside the membrane. Under the excitation of an externally applied AC magnetic field, the magnetically-soft strip produces a higher-order magnetic signature that can be remotely detected with an external receiving coil. As ambient pressure varies, the pressure membrane deflects, altering the separation distance between the magnetically-soft strip and the permanent magnet. This shifts the higher-order harmonic signal, allowing for detection of pressure change as a function of harmonic shifting. The wireless, passive nature of this sensor technology allows for continuous long-term pressure monitoring, particularly useful for biomedical applications such as monitoring pressure in aneurysm sac and sphincter of Oddi. In addition to demonstrating its pressure sensing capability, an animal model was used to investigate the efficacy and feasibility of the pressure sensor in a biological environment. http://www.mdpi.com/2079-6374/1/4/134 Mon, 17 Oct 2011 00:00:00 CEST Biosensors 2011-10-17 1 4 Article 134 152 2079-6374 Design, Fabrication, and Implementation of a Wireless, Passive Implantable Pressure Sensor Based on Magnetic Higher-Order Harmonic Fields 2011-10-17 doi: 10.3390/bios1040134 Ee Lim Tan Andrew J. DeRouin Brandon D. Pereles Keat Ghee Ong http://www.mdpi.com/2079-6374/1/3/118 Diamond is a material of interest due to its unique combination of properties, including its chemical inertness and biocompatibility. Polycrystalline diamond (poly-C) has been used in experimental biosensors that utilize electrochemical methods and antigen-antibody binding for the detection of biological molecules. Boron-doped poly-C electrodes have been found to be very advantageous for electrochemical applications due to their large potential window, low background current and noise, and low detection limits (as low as 500 fM). The biocompatibility of poly-C is found to be comparable, or superior to, other materials commonly used for implants, such as titanium and 316 stainless steel. We have developed a diamond-based, neural microelectrode-array (MEA), due to the desirability of poly-C as a biosensor. These diamond probes have been used for in vivo electrical recording and in vitro electrochemical detection. Poly-C electrodes have been used for electrical recording of neural activity. In vitro studies indicate that the diamond probe can detect norepinephrine at a 5 nM level. We propose a combination of diamond micro-machining and surface functionalization for manufacturing diamond pathogen-microsensors. http://www.mdpi.com/2079-6374/1/3/118 Mon, 15 Aug 2011 00:00:00 CEST Biosensors 2011-08-15 1 3 Article 118 133 2079-6374 Polycrystalline-Diamond MEMS Biosensors Including Neural Microelectrode-Arrays 2011-08-15 doi: 10.3390/bios1030118 Michael W. Varney Dean M. Aslam Abed Janoudi Ho-Yin Chan Donna H. Wang http://www.mdpi.com/2079-6374/1/3/107 Alanine aminotransaminase (ALT), is an enzyme that normally resides in serum and body tissues, especially in the liver. It is released into the serum as a result of tissue injury; hence the concentration of ALT in the serum may be increased with acute damage to hepatic cells. A single use, disposable biosensor, comprising iridium nano-particle as catalyst dispersed on carbon paste, has been developed for the determination of ALT concentration. The biosensor is based on quantifying H2O2 concentration produced by a serial of ALT enzymatic reactions. It operates well at room temperature in different physiological fluids: phosphate buffer, calf serum and human serum for ALT concentration of 0–544 ng/mL. Experimental results in human serum are compared to those obtained by spectrophotometric assays with excellent agreement. Therefore, the Ir/C biosensor shows good relationship on the dilution of concentrated ALT clinical applications. http://www.mdpi.com/2079-6374/1/3/107 Tue, 12 Jul 2011 00:00:00 CEST Biosensors 2011-07-12 1 3 Article 107 117 2079-6374 Determination of Alanine Aminotransferase with an Electrochemical Nano Ir-C Biosensor for the Screening of Liver Diseases 2011-07-12 doi: 10.3390/bios1030107 Chang-Jung Hsueh Joanne H. Wang Liming Dai Chung-Chiun Liu http://www.mdpi.com/2079-6374/1/3/93 Triacetone triperoxide (TATP) is a primary explosive, which was used in various terrorist attacks in the past. For the development of biosensors, immunochemical µ-TAS, electronic noses, immunological test kits, or test strips, the availability of antibodies of high quality is crucial. Recently, we presented the successful immunization of mice, based on the design, synthesis, and conjugation of a novel TATP derivative. Here, the long-term immunization of rabbits is shown, which resulted in antibodies of extreme selectivity and more than 1,000 times better affinity in relation to the antibodies from mice. Detection limits below 10 ng L−1 (water) were achieved. The working range covers more than four decades, calculated from a precision profile. The cross-reactivity tests revealed an extraordinary selectivity of the antibodies—not a single compound could be identified as a relevant cross-reactant. The presented immunoreagent might be a major step for the development of highly sensitive and selective TATP detectors particularly for security applications. http://www.mdpi.com/2079-6374/1/3/93 Thu, 07 Jul 2011 00:00:00 CEST Biosensors 2011-07-07 1 3 Article 93 106 2079-6374 A Novel Immunoreagent for the Specific and Sensitive Detection of the Explosive Triacetone Triperoxide (TATP) 2011-07-07 doi: 10.3390/bios1030093 Maria Astrid Walter Ulrich Panne Michael G. Weller http://www.mdpi.com/2079-6374/1/3/70 Label-free biomolecular interaction analysis is an important technique to study the chemical binding between e.g., protein and protein or protein and small molecule in real-time. The parameters obtained with this technique, such as the affinity, are important for drug development. While the surface plasmon resonance (SPR) instruments are most widely used, new types of sensors are emerging. These developments are generally driven by the need for higher throughput, lower sample consumption or by the need of complimentary information to the SPR data. This review aims to give an overview about a wide range of sensor transducers, the working principles and the peculiarities of each technology, e.g., concerning the set-up, sensitivity, sensor size or required sample volume. Starting from optical technologies like the SPR and waveguide based sensors, acoustic sensors like the quartz crystal microbalance (QCM) and the film bulk acoustic resonator (FBAR), calorimetric and electrochemical sensors are covered. Technologies long established in the market are presented together with those newly commercially available and with technologies in the early development stage. Finally, the commercially available instruments are summarized together with their sensitivity and the number of sensors usable in parallel and an outlook for potential future developments is given. http://www.mdpi.com/2079-6374/1/3/70 Fri, 01 Jul 2011 00:00:00 CEST Biosensors 2011-07-01 1 3 Review 70 92 2079-6374 Review of Transducer Principles for Label-Free Biomolecular Interaction Analysis 2011-07-01 doi: 10.3390/bios1030070 Martin Nirschl Florian Reuter Janos Vörös http://www.mdpi.com/2079-6374/1/2/58 In this article, we describe the kinetic ELISA of Blue Tongue and Epizootic Hemorrhagic Disease viral antibodies in microfluidic channels by monitoring the rate of generation of the enzyme reaction product under static conditions. It has been shown that this format of the immunoassay allows very reliable quantitation of the target species using inexpensive glass microchips and a standard epifluorescence microscope system coupled to a CCD camera. For the viral antibodies assayed here, the limit of detection (LOD) for the analyte concentration in our microchips was established to be 3–5 times lower than that obtained on commercial microwell plates using a fiftieth of the sample volume and less than a third of the incubation time. Our analyses further show that when compared to the end-point ELISA format, the kinetic mode of this assay yields an improvement in the LOD by over an order of magnitude in microfluidic devices. This benefit is primarily realized as the observed variation in the background fluorescence (signal at the start of the enzyme reaction period) was significantly larger than that in the rate of signal generation upon repeating these assays in different microchannels/microchips. Because the kinetic ELISA results depend only on the latter quantity, the noise level in them was substantially lower compared to that in its end-point counterpart in which the absolute fluorescence measurements are of greater significance. While a similar benefit was also recorded through implementation of kinetic ELISAs on the microwell platform, the improvement in LOD registered in that system was not as significant as was observed in the case of microfluidic assays. http://www.mdpi.com/2079-6374/1/2/58 Fri, 17 Jun 2011 00:00:00 CEST Biosensors 2011-06-17 1 2 Article 58 69 2079-6374 Kinetic ELISA in Microfluidic Channels 2011-06-17 doi: 10.3390/bios1020058 Naoki Yanagisawa Debashis Dutta http://www.mdpi.com/2079-6374/1/2/46 By simultaneously measuring the bulk media and electrode interface voltages of a yeast (Saccharomyces cerevisiae) suspension subjected to an AC voltage, a yeast-dependent nonlinear response was found only near the current injection electrodes. Computer simulation of yeast near a current injection electrode found an enhanced voltage drop across the yeast near the electrode due to slowed charging of the electrode interfacial capacitance. This voltage drop is sufficient to induce conformation change in membrane proteins. Disruption of the mitochondrial electron transport chain is found to significantly change the measured nonlinear current response, suggesting nonlinear impedance can be used as a non-invasive probe of cellular metabolic activity. http://www.mdpi.com/2079-6374/1/2/46 Mon, 11 Apr 2011 00:00:00 CEST Biosensors 2011-04-11 1 2 Article 46 57 2079-6374 Nonlinear Impedance of Whole Cells Near an Electrode as a Probe of Mitochondrial Activity 2011-04-11 doi: 10.3390/bios1020046 Akilan Palanisami George T. Mercier Jie Fang John H. Miller Jr. http://www.mdpi.com/2079-6374/1/2/36 This study aims to measure the effect of toxic aqueous solutions of metals on the mobility of Artemia salina nauplii by using digital image processing. The instrument consists of a camera with a macro lens, a dark chamber, a light source and a laptop computer. Four nauplii were inserted into a macro cuvette, which contained copper, cadmium, iron and zinc ions at various concentrations. The nauplii were then filmed inside the dark chamber for two minutes and the video sequence was processed by a motion tracking algorithm that estimated their mobility. The results obtained by this system were compared to the mortality assay of the Artemia salina nauplii. Despite the small number of tested organisms, this system demonstrates great sensitivity in quantifying the mobility of the nauplii, which leads to significantly lower EC50 values than those of the mortality assay. Furthermore, concentrations of parts per trillion of toxic compounds could be detected for some of the metals. The main novelty of this instrument relies in the sub-pixel accuracy of the tracking algorithm that enables robust measurement of the deterioration of the mobility of Artemia salina even at very low concentrations of toxic metals. http://www.mdpi.com/2079-6374/1/2/36 Mon, 28 Mar 2011 00:00:00 CEST Biosensors 2011-03-28 1 2 Article 36 45 2079-6374 Monitoring the Effect of Metal Ions on the Mobility of Artemia salina Nauplii 2011-03-28 doi: 10.3390/bios1020036 Varvara Kokkali Ioannis Katramados Jeffrey D. Newman http://www.mdpi.com/2079-6374/1/1/23 Here we report the fabrication and characterization of pH sensors using aligned single-walled carbon nanotubes (SWNTs). The SWNTs are dispersed in deionized (DI) water after chemical functionalization and filtration. They are deposited and organized on silicon substrates with the dielectrophoresis process. Electrodes with “teeth”-like patterns—fabricated with photolithography and wet etching—are used to generate concentrated electric fields and strong dielectrophoretic forces for the SWNTs to deposit and align in desired locations. The device fabrication is inexpensive, solution-based, and conducted at room temperature. The devices are used as pH sensors with the electrodes as the testing pads and the dielectrophoretically captured SWNTs as the sensing elements. When exposed to aqueous solutions with various pH values, the SWNTs change their resistance accordingly. The SWNT-based sensors demonstrate a linear relationship between the sensor resistance and the pH values in the range of 5–9. The characterization of multiple sensors proves that their pH sensitivity is highly repeatable. The real-time data acquisition shows that the sensor response time depends on the pH value, ranging from 2.26 s for the pH-5 solution to 23.82 s for the pH-9 solution. The long-term stability tests illustrate that the sensors can maintain their original sensitivity for a long period of time. The simple fabrication process, high sensitivity, and fast response of the SWNT-based sensors facilitate their applications in a wide range of areas. http://www.mdpi.com/2079-6374/1/1/23 Mon, 31 Jan 2011 00:00:00 CET Biosensors 2011-01-31 1 1 Article 23 35 2079-6374 Dielectrophoresis Aligned Single-Walled Carbon Nanotubes as pH Sensors 2011-01-31 doi: 10.3390/bios1010023 Pengfei Li Caleb M. Martin Kan Kan Yeung Wei Xue http://www.mdpi.com/2079-6374/1/1/13 Nonlinear dielectric spectroscopy (NDS) is a non-invasive probe of cellular metabolic activity with potential application in the development of whole-cell biosensors. However, the mechanism of NDS interaction with metabolic membrane proteins is poorly understood, partly due to the inherent complexity of single cell organisms. Here we use the light-activated electron transport chain of spinach thylakoid membrane as a model system to study how NDS interacts with metabolic activity. We find protein modification, as opposed to membrane pump activity, to be the dominant source of NDS signal change in this system. Potential mechanisms for such protein modifications include reactive oxygen species generation and light-activated phosphorylation. http://www.mdpi.com/2079-6374/1/1/13 Mon, 31 Jan 2011 00:00:00 CET Biosensors 2011-01-31 1 1 Article 13 22 2079-6374 Nonlinear Dielectric Spectroscopy as an Indirect Probe of Metabolic Activity in Thylakoid Membrane 2011-01-31 doi: 10.3390/bios1010013 Jie Fang Akilan Palanisami Kimal Rajapakshe William R. Widger John H. Miller http://www.mdpi.com/2079-6374/1/1/4 With the rapid growth of Biological/Biomedical MicroElectroMechanical Systems (BioMEMS) and microfluidic-based lab-on-a-chip (LOC) technology to biological and biomedical research and applications, demands for educated and trained researchers and technicians in these fields are rapidly expanding. Universities are expected to develop educational plans to address these specialized needs in BioMEMS, microfluidic and LOC science and technology. A course entitled BioMEMS and Lab-on-a-Chip was taught recently at the senior undergraduate and graduate levels in the Department of Computer Science and Electrical Engineering at West Virginia University (WVU). The course focused on the basic principles and applications of BioMEMS and LOC technology to the areas of biomedicine, biology, and biotechnology. The course was well received and the enrolled students had diverse backgrounds in electrical engineering, material science, biology, mechanical engineering, and chemistry. Student feedback and a review of the course evaluations indicated that the course was effective in achieving its objectives. Student presentations at the end of the course were a highlight and a valuable experience for all involved. The course proved successful and will continue to be offered regularly. This paper provides an overview of the course as well as some development and future improvements. http://www.mdpi.com/2079-6374/1/1/4 Thu, 20 Jan 2011 00:00:00 CET Biosensors 2011-01-20 1 1 Article 4 12 2079-6374 BioMEMS and Lab-on-a-Chip Course Education at West Virginia University 2011-01-20 doi: 10.3390/bios1010004 Yuxin Liu http://www.mdpi.com/2079-6374/1/1/1 The journal Biosensors has been started as a peer-reviewed, open access journal. As editors, we believe that it will fulfill an important role in the community of researchers and developers in the field of biosensors. The addition of a “free access” journal to the existing, high quality publications in this field is something that we believe is very important in a field which is now so entwined with commercial activity and where researchers aim, not only at academic research, but on the development of products at a potentially massive scale. For these researchers, it is important that they can publish their results in a journal that guarantees quality that comes from peer-review, but that at the same time breaks the traditional boundaries of academic journals which need a subscription or a pay-per-view option to access the published data. http://www.mdpi.com/2079-6374/1/1/1 Wed, 19 Jan 2011 00:00:00 CET Biosensors 2011-01-19 1 1 Editorial 1 3 2079-6374 Welcome to Biosensors: A New Open-Access Journal 2011-01-19 doi: 10.3390/bios1010001 Jeffrey D. Newman