Development of closed bipolar electrode based L-lactate sensor employing quasi-direct electron transfer type enzyme with cyclic voltammetry

Herein, we present a proof-of-concept of an enzyme sensor combining closed bipolar electrode system with quasi-direct electron transfer (DET) type enzyme. The closed bipolar electrode system was tested using cyclic voltammetry, with L-lactate as a model substrate. L-Lactate was detected through measurement of the change in junction potential across the bipolar electrode. This change in junction potential was caused by reduction of amino reactive phenazine ethosulfate conjugated to Aerococcus vilidans derived engineered L-lactate oxidase (AvLOx) which shows a quasi-DET signal. Using the closed bipolar electrode system allowed simultaneous measuring using cyclic voltammetry and open circuit potential (OCP) and achieved a limit of detection of 400 μM and 76.2 μM lactate respectively. The sensor was then demonstrated to perform with equivalent sensitivity using OCP across varying surface areas. To the best of our knowledge this is the first time a closed bipolar electrode system has been used with an enzyme which is capable of quasi-direct or direct electron transfer. This work can be expanded further to other enzymes capable of directly altering the junction potential of an electrode surface.

Development of the BioBattery: A novel enzyme fuel cell using a multicopper oxidase as an anodic enzyme

This work presents the development of an enzyme fuel cell, termed "BioBattery", that utilizes multicopper oxidases as the anodic enzyme in a non-diffusion limited system. We evaluated various enzyme variants as the anode, including multicopper oxidase from Pyrobaculum aerophilum, laccase from Trametes versicolor, and bilirubin oxidase from Myrothecium verrucaria. Several combinations of cathodes were also examined, focusing on the reduction of oxygen as the primary electron acceptor. The optimal pairing used multicopper oxidase from Pyrobaculum aerophilum as the anode and amine reactive phenazine ethosulfate modified bovine serum albumin as the cathode. BioBattery was integrated with our previously developed BioCapacitor, proving capable of consistently powering a 470 μF capacitor, positioning it as a modular power source for wearable and implantable systems. This research work addresses and overcomes some of the fundamental limitations seen in enzyme fuel cells, where power and current are often limited by substrate accessibility to the active electrode surface. (152 words).

Development of Direct Electron Transfer-Type Extended Gate Field Effect Transistor Enzymatic Sensors for Metabolite Detection

In this work, direct electron transfer (DET)-type extended gate field effect transistor (EGFET) enzymatic sensors were developed by employing DET-type or quasi-DET-type enzymes to detect glucose or lactate in both 100 mM potassium phosphate buffer and artificial sweat. The system employed either a DET-type glucose dehydrogenase or a quasi-DET-type lactate oxidase, the latter of which was a mutant enzyme with suppressed oxidase activity and modified with amine-reactive phenazine ethosulfate. These enzymes were immobilized on the extended gate electrodes. Changes in the measured transistor drain current (ID) resulting from changes to the working electrode junction potential (φ) were observed as glucose and lactate concentrations were varied. Calibration curves were generated for both absolute measured ID and ΔID (normalized to a blank solution containing no substrate) to account for variations in enzyme immobilization and conjugation to the mediator and variations in reference electrode potential. This work resulted in a limit of detection of 53.9 μM (based on ID) for glucose and 2.12 mM (based on ID) for lactate, respectively. The DET-type and Quasi-DET-type EGFET enzymatic sensor was then modeled using the case of the lactate sensor as an equivalent circuit to validate the principle of sensor operation being driven through OCP changes caused by the substrate-enzyme interaction. The model showed slight deviation from collected empirical data with 7.3% error for the slope and 8.6% error for the y-intercept.

Cell size and actin architecture determine force generation in optogenetically activated cells

Adherent cells use actomyosin contractility to generate mechanical force and to sense the physical properties of their environment, with dramatic consequences for migration, division, differentiation, and fate. However, the organization of the actomyosin system within cells is highly variable, with its assembly and function being controlled by small GTPases from the Rho family. To understand better how activation of these regulators translates into cell-scale force generation in the context of different physical environments, here we combine recent advances in non-neuronal optogenetics with micropatterning and traction force microscopy on soft elastic substrates. We find that, after whole-cell RhoA activation by the CRY2/CIBN optogenetic system with a short pulse of 100 ms, single cells contract on a minute timescale in proportion to their original traction force, before returning to their original tension setpoint with near perfect precision, on a longer timescale of several minutes. To decouple the biochemical and mechanical elements of this response, we introduce a mathematical model that is parametrized by fits to the dynamics of the substrate deformation energy. We find that the RhoA response builds up quickly on a timescale of 20 s, but decays slowly on a timescale of 50 s. The larger the cells and the more polarized their actin cytoskeleton, the more substrate deformation energy is generated. RhoA activation starts to saturate if optogenetic pulse length exceeds 50 ms, revealing the intrinsic limits of biochemical activation. Together our results suggest that adherent cells establish tensional homeostasis by the RhoA system, but that the setpoint and the dynamics around it are strongly determined by cell size and the architecture of the actin cytoskeleton, which both are controlled by the extracellular environment.

Development of Electrochemical Methods to Enzymatically Detect Lactate and Glucose Using Imaginary Impedance for Enhanced Management of Glycemic Compromised Patients

Lactate is an important biological marker that can provide valuable information for patients who have experienced a traumatic injury. Additionally, when coupled with glucose, the severity and likely prognosis of a traumatic injury can be determined. Because monitoring various markers proves useful in diagnosis and treatment of trauma patients, monitoring both glucose and lactate simultaneously may be especially useful for diabetic patients who have suffered a traumatic injury. Previously, using electrochemical impedance spectroscopy (EIS), a sensor capable of measuring two affinity-based biomarkers simultaneously was demonstrated using the biomarker's specific optimal frequency to develop a deconvolution algorithm, which allowed for the measurement of two biomarkers from a single signal. Herein, while developing an EIS lactate sensor, dual enzymatic biomarker detection of lactate and glucose via EIS was also attempted. Both biomarkers were validated individually with the lactate sensor being additionally validated on whole blood samples. The EIS lactate biosensor achieved a range of detection from 0 to 32 mM of lactate and the glucose sensor a range of 0-100 mg/dL of glucose, which are representative of the likely physiological ranges that trauma patients experience. However, the preliminary attempt of dual marker detection was unsuccessful due to suspected accumulation of reduced redox probe on the surface of the self-assembled monolayer (SAM). Individually, the optimal frequency of lactate was determined to be 69.75 Hz and that of glucose was determined to be 31.5 Hz. However, when combined onto one sensor, no discernable optimal frequency could be determined which again was suspected to be due to the accumulation of the reduced redox probe at the surface of the SAM.

Development Toward a Triple-Marker Biosensor for Diagnosing Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of death in the United States and is responsible for 30% of all deaths globally. The diagnosis and management of CVD requires monitoring of multiple biomarkers, which comprehensively represents the state of the disease. However, many assays for cardiac biomarkers today are complicated and laborious to perform. Rapid and sensitive biosensors capable of giving accurate measurements of vital cardiac biomarkers without complex procedures are thus in high demand. In the work presented below, rapid, label-free biosensor prototypes for three Food and Drug Administration-approved biomarkers are reported: B-type natriuretic peptide (BNP), cardiac troponin I (cTnI), and C-reactive protein (CRP). The sensors were prepared by immobilizing each biomarker's antibody onto gold working electrodes with platinum counter and silver/silver chloride reference electrodes. The sensors were tested using electrochemical impedance spectroscopy (EIS), a femto-molar sensitive technique capable of label-free, multi-marker detection if a biomarker's optimal frequency (OF) can be identified. The OFs of BNP, cTnI, and CRP were found to be 1.74, 37.56, and 253.9 Hz, respectively. The performance of the BNP biosensor was also evaluated in blood and achieved clinically relevant detection limits of 100 pg/mL.

Facilitating Earlier Diagnosis of Cardiovascular Disease through Point-of-Care Biosensors: A Review

Cardiovascular disease (CVD) accounts for 30% of all global deaths and is predicted to dominate in the coming years, despite vast improvements in medical technology. Current clinical methods of assessing an individual's cardiovascular health include blood tests to monitor relevant biomarker levels as well as varying imaging modalities such as electrocardiograms, computed tomography, and angiograms to assess vasculature. As informative as these tools are, they each require lengthy scheduling, preparation, and highly trained personnel to interpret the results before any information is accessible to patients, often leading to delayed treatment, which can be fatal. A point-of-care (POC) sensor platform is thus paramount in rapid and early diagnosis of CVD. Among the many POC detection platforms, including established optical and mechanical methods, electrochemical-based detection mechanisms have become increasingly desirable because of their superior sensitivity, low cost, and label-free detection. Specifically, electrochemical impedance spectroscopy (EIS) has demonstrated remarkable abilities in low-level (femtomolar) detection of several clinically useful biomarkers and has been reported in CVD diagnostic applications. In this review, we provide an in-depth overview of prevalent CVD diseases and clinically relevant proteomic biomarkers for assessing them. Subsequently, we discuss the ongoing development of POC sensors for CVD, highlighting the current clinical gold standard, potential alternative modalities, and electrochemical methodologies previously successful in quantifying specific biomarkers approved by the Food and Drug Administration (FDA). A discussion of EIS highlighting the attributes and capabilities of novel analysis algorithms is included to showcase the possibility of simultaneous dual-marker detection.

The electrochemical behavior of a FAD dependent glucose dehydrogenase with direct electron transfer subunit by immobilization on self-assembled monolayers

Continuous glucose monitoring (CGM) is a vital technology for diabetes patients by providing tight glycemic control. Currently, many commercially available CGM sensors use glucose oxidase (GOD) as sensor element, but this enzyme is not able to transfer electrons directly to the electrode without oxygen or an electronic mediator. We previously reported a mutated FAD dependent glucose dehydrogenase complex (FADGDH) capable of direct electron transfer (DET) via an electron transfer subunit without involving oxygen or a mediator. In this study, we investigated the electrochemical response of DET by controlling the immobilization of DET-FADGDH using 3 types of self-assembled monolayers (SAMs) with varying lengths. With the employment of DET-FADGDH and SAM, high current densities were achieved without being affected by interfering substances such as acetaminophen and ascorbic acid. Additionally, the current generated from DET-FADGDH electrodes decreased with increasing length of SAM, suggesting that the DET ability can be affected by the distance between the enzyme and the electrode. These results indicate the feasibility of controlling the immobilization state of the enzymes on the electrode surface.

Enhancing Glycemic Control via Detection of Insulin Using Electrochemical Impedance Spectroscopy

BACKGROUND

Currently, glycemic management for individuals with diabetes mellitus involves monitoring glucose only, which is insufficient as glucose metabolism involves other biomarkers such as insulin. Monitoring additional biomarkers alongside glucose has been proposed to improve glycemic control. In this work, the development of a rapid and label-free insulin biosensor with high sensitivity and accuracy is presented. The insulin sensor prototype also serves as a prior study for a multimarker sensing platform technology that can further improve glycemic control in the future.

METHODS

Electrochemical impedance spectroscopy was used to identify an optimal frequency specific to insulin detection on a gold disk electrode with insulin antibody immobilized, which was accomplished by conjugating the primary amines of insulin antibody to the carboxylic bond of the self-assembling monolayer on the gold surface. After blocking with ethanolamine, the insulin physiological concentration gradient was tested. The imaginary impedance was correlated to insulin concentration and the results were compared with standard equivalent circuit analysis and correlation of charge transfer resistance to target concentration.

RESULTS

The optimal frequency of insulin is 810.5 Hz, which is characterized by having the highest sensitivity and sufficient specificity. The lower limit of detection was 2.26 [Formula: see text] which is comparable to a standard and better than traditional approaches.

CONCLUSION

An insulin biosensor prototype capable of detecting insulin in physiological range without complex data normalization was developed. This prototype will be the ground works of a multimarker platform sensor technology for future all-in-one glycemic management sensors.

Feasibility in the development of a multi-marker detection platform

A feasibility study for a label-free, multi-marker single sensor using electrochemical impedance spectroscopy (EIS), imaginary impedance, and a signal decoupling technique is reported. To our knowledge, this is the first reported attempt of using imaginary impedance for biomarker detection and multi-marker detection. The electrochemical responses of purified low and high density lipoproteins (LDL and HDL, respectively) were first individually characterized through the immobilization of their molecular recognition elements (MREs) onto gold disk electrodes (GDEs). The co-immobilization was performed by immobilizing the MREs of both LDL and HDL on the same GDE, which was then used to detect LDL and HDL simultaneously in mixed solution. Previous individual purified responses were then used to de-convolute the mixed response, when the two biomarkers were detected in mixed solutions. The optimal frequencies of LDL and HDL were found to be 81.38Hz and 5.49Hz, respectively, which shifted to 175.8Hz and 3.74Hz under co-immobilized conditions. After comparing the electrochemical signal in complex and imaginary impedance, imaginary impedance was found to be more suitable for multi-marker detection purposes. Since imaginary impedance is related to capacitance, electric displacement, relative permittivity, and effective capacitance were derived to elucidate the theory of optimal frequency. This work shows that EIS has the potential for multi-marker detection and can be extended to monitor other complex diseases such as diabetes mellitus for better management and diagnostic purposes.

Phospholipase C-dependent control of cardiac calcium homeostasis involves a TRPC3-NCX1 signaling complex

OBJECTIVE

Members of the classical transient receptor potential protein (TRPC) family are considered as key components of phospholipase C (PLC)-dependent Ca2+ signaling. Previous results obtained in the HEK 293 expression system suggested a physical and functional coupling of TRPC3 to the cardiac-type Na+/Ca2+ exchanger, NCX1 (sodium calcium exchanger 1). This study was designed to test for expression of TRPC3 (transient receptor potential channel 3) and for the existence of a native TRPC3/NCX1 signaling complex in rat cardiac myocytes.

METHODS

Protein expression and cellular distribution were determined by Western blot and immunocytochemistry. Protein-protein interactions were investigated by reciprocal co-immunoprecipitation and glutathione S-transferase (GST)-pulldown experiments. Recruitment of protein complexes into the plasma membrane was assayed by surface biotinylation. The functional role of TRPC3 was investigated by fluorimetric recording of angiotensin II-induced calcium signals employing a dominant negative knockdown strategy.

RESULTS

TRPC3 immunoreactivity was observed in surface plasma membrane regions and in an intracellular membrane system. Co-immunolabeling of TRPC3 and NCX1 indicated significant co-localization of the two proteins. Both co-immunoprecipitation and GST-pulldown experiments demonstrated association of TRPC3 with NCX1. PLC stimulation was found to trigger NCX-mediated Ca2+ entry, which was dependent on TRPC3-mediated Na+ loading of myocytes. This NCX-mediated Ca2+ signaling was significantly suppressed by expression of a dominant negative fragment of TRPC3. PLC stimulation was associated with increased membrane presentation of both TRPC3 and NCX1.

CONCLUSION

These results suggest a PLC-dependent recruitment of a TRPC3-NCX1 complex into the plasma membrane as a pivotal mechanism for the control of cardiac Ca2+ homeostasis.

Primary ciliary dyskinesia: a genome-wide linkage analysis reveals extensive locus heterogeneity

Primary ciliary dyskinesia (PCD), or immotile cilia syndrome (ICS), is an autosomal recessive disorder affecting ciliary movement with an incidence of 1 in 20000-30000. Dysmotility to complete immotility of cilia results in a multisystem disease of variable severity with recurrent respiratory tract infections leading to bronchiectasis and male subfertility. Ultrastructural defects are present in ciliated mucosa and spermatozoa. Situs inversus (SI) is found in about half of the patients (Kartagener syndrome). We have collected samples from 61 European and North American families with PCD. A genome-wide linkage search was performed in 31 multiplex families (169 individuals including 70 affecteds) using 188 evenly spaced (19cM average interval) polymorphic markers. Both parametric (recessive model) and non-parametric (identity by descent allele sharing) linkage analyses were used. No major locus for the majority of the families was identified, although the sample was powerful enough to detect linkage if 40% of the families were linked to one locus. These results strongly suggest extensive locus heterogeneity. Potential genomic regions harbouring PCD loci were localised on chromosomes 3p, 4q, 5p, 7p, 8q, 10p, 11q, 13q, 15q, 16p, 17q and 19q. Linkage analysis using PCD families with a dynein arm deficiency provided 'suggestive' evidence for linkage to chromosomal regions 8q, 16pter, while analyses using only PCD families with situs inversus resulted in 'suggestive' scores for chromosomes 8q, and 19q.

[Maternal morbidity after abdominal cesarean section in relation to bacterial amniotic fluid colonization and premature rupture of fetal membranes]

At the time of Caesarean section, amniotic fluid was collected transabdominally from 1025 patients. In 990 patients cultures were performed on the amniotic fluid. The incidence of Caesarean section of all patients was 16.1%, the perinatal mortality in all patients 0.61%, in cases of Caesarean section 1.93%. The influence of bacterial colonisation in the amniotic cavity was analyzed with respect to premature ruptured membranes and frequency of vaginal examinations on the maternal post-operative morbidity (wound-seroma and abscess 2.4%, febrile morbidity 17%, urinary tract infection 19%). Bacterial contamination was present in 33.3% of the amniotic fluid or uterine cavity, after ruptured membranes in 44.3%, without ruptured membranes in 23.35%. There is a significant influence of the positive cultured amniotic fluid on the wound healing and on the febrile morbidity, while the urinary tract infection has been not influenced. The bacterial contamination of the amniotic fluid is correlated to the frequency of vaginal examination and the presence of ruptured membranes. The following microbiologic isolates were found in the amniotic fluids: Staphylococcus epidermidis 36.38%, Streptococcus B 12.23%, Streptococcus D 10.3%, Escherichia coli 8.42%, Staphylococcus aureus 7.88%, Peptococci 3.26%, Streptococcus salivarius 2.99%, Bacteroides 2.4%. According to these data, patients with ruptured membranes of an interval of more than 12 hrs and with more than 7 vaginal examinations could be selected for antibiotic prophylaxis to achieve a reduction in febrile morbidity and in wound infection.

[Hemodynamic effects of the induction of general anesthesia after low thoracic epidural anesthesia]

Sixteen ASA 1 or 2 patients scheduled for abdominal surgery were included in the study after they had given their informed consent. Thirty minutes after starting a low-thoracic epidural anaesthesia (median level of sensitivity loss: T5), the patients were randomly given an intravenous bolus injection of either thiopentone (4 mg.kg-1, n = 8) or etomidate (0.5 mg.-1, n = 8), associated with succinylcholine 1 mg.kg-1. One minute after induction of general anaesthesia, the patients were intubated and mechanically ventilated (V(T) 8 ml.kg-1, rate 12 c.min-1). Mean arterial blood pressure (MAP) (oscillometric method), cardiac output (CO) (transthoracic bioimpedance) and heart rate were recorded semi-continuously. Total peripheral resistances (TPR) were calculated using the formula TPR = (MA/CO)*80. There were no differences between the groups in patient age, height, weight, and cardiovascular consequences of epidural anaesthesia. After anaesthetic induction and before endotracheal intubation, there was a slight decrease in CO in both groups, without any change in MAP. After intubation, MAP increased in both groups through peripheral vasoconstriction, whereas CO did not increase further. A significant tachycardia was occurred only seen in the thiopentone group, before and after tracheal intubation. This study showed that thiopentone and etomidate were suitable drugs for anaesthetic induction in a patient under epidural blockade. However, the absence of tachycardia following etomidate may be beneficial in cardiac patients. The monitoring of cardiac output determinants during thiopentone and etomidate anaesthesia require further invasive investigations.

[Effects of lidocaine on arterial and venous circulation of limbs in man]

The effects of intravenous lidocaine on limb arteries and veins were investigated in a placebo-controlled study. Seven young healthy volunteers, 23 to 28-years-old, were included. Electrocardiogram, arterial pressure and arm and leg blood flows were recorded continuously. Systolic and diastolic blood pressures were measured in the left arm by finger photoplethysmography. Limb blood flow and the limb venous system were studied by venous occlusive plethysmography. The venous parameters studied were venous tone, lowest closing pressure, venous volume at 30 mmHg, and venous distensibility. After an initial bolus of 1.5 mg.kg-1 lidocaine had been given, 30, and then 60, micrograms.kg-1.min-1 were given for one hour each. Plasma noradrenaline and serum lidocaine titres were measured before giving the lidocaine, and at the end of each one hour period. Placebo consisted in a two hour infusion of 0.25 ml.min-1 normal saline. Lidocaine titres were 1.64 +/- 0.40 microgram.ml-1 after one hour, and 2.55 +/- 0.69 microgram.ml-1 after two hours. Lidocaine increased vascular resistances in both the forearm (+81% to +93%) and the calf (+38% to +57%). There was a concomitant increase in mean arterial blood pressure (+21% to +28%) without any change in heart rate. There was a significant dose-dependent increase in plasma noradrenaline levels during the second period of the lidocaine infusion with respect to the preinfusion period and the same period during the placebo infusion. Venous capacitance measured before any infusion had been started was greater in the leg than in the arm.(ABSTRACT TRUNCATED AT 250 WORDS)

[The effect of housing on the development of calluses and subcutaneous mucus cysts on the limbs of swine]

Extremities of pigs often show swelling of various size and consistency. The aim of the present investigation was to determine the cause of the swelling with special emphasis on housing conditions. A total of 168 animals kept on slatted and/or partly slatted floors and 55 pigs kept on straw were examined. The swelling was partially caused by connective tissue proliferation only, but more often consisted of non inflamed subcutaneous bursae. Skeletal changes near the periost could never be seen. In pigs kept on straw weals and subcutaneous bursae practically never developed, whereas in animals kept on concrete, these changes did occur more frequently and were more pronounced with time.

Ultrastructure of somatotrophs of rats with median eminence lesions: studies in basal conditions and after thyrotropin-releasing hormone stimulation

Anterior pituitaries from female Sprague-Dawley rats (160-200 g b.w) bearing electrolytic lesions of the median eminence were qualitatively and quantitatively investigated by electron microscopy and the findings compared with those from intact animals or sham-operated controls. This study was performed in basal conditions and after stimulation with thyrotropin-releasing hormone. Animals with lesions showed a reduction of both the number of somatotrophic cells and growth hormone granules. After injection of thyrotropin-releasing hormone exocytosis of growth hormone granules from somatotrophs was frequent in rats with lesions of the median eminence but rare in sham-operated animals. The differences were statistically significant.

Light and electron microscopic studies of thyrotrophin releasing hormone-induced growth hormone and prolactin release in hypophysectomized rats bearing an ectopic pituitary gland

A light microscopic and ultrastructural study of anterior pituitary glands transplanted under the kidney capsule of hypophysectomized rats was performed, in basal conditions and after stimulation with thyrotrophin releasing hormone, at various intervals (24 h-2 months) after transplantation. Confirming previous biochemical findings, the results suggest that with time, somatotrophs acquire sensitivity to thyrotrophin releasing hormone and respond with increased exocytosis at doses that were found ineffective in pituitary glands in situ. Thyrotrophin releasing hormone stimulation did not seem to influence the morphology of prolactin cells, which were already highly active under basal conditions at all time intervals.

Ultrastructural study of the adenohypophysis of the Chinese hamster

The adenohypophysis of normal Chinese hamsters of both sexes was examined ultrastructurally. Organs were fixed by intravascular perfusion with S-collidine-buffered glutaraldehyde solution. Seven types of cells were differentiated and, according to morphological characteristics, classified as (1) mammotropes, with very large (400-800 nm) polymorphous secretory granules; (2) somatotropes, either in the storage phase with numerous large, dense granules (average 300 nm), or in the hormone synthesis phase, with abundant endoplasmic reticulum and large Golgi apparatus; (3) corticotropes, with irregular cell shape, and granules (average 160 nm) arranged in lines parallel to the cell membrane; (4) FSH gonadotropes, with abundant and dilated endoplasmic reticulum, and granules (190-320 nm) uniformly distributed in the cytoplasm; (5) LH gonadotropes, with granules (120-220 nm) of varied density; (6) thyrotropes, with irregular cell shape and very small granules (120-160 nm), and (7) agranulated cells. The ultrastructure of the adenohypophysis of the Chinese hamster corresponds closely with observations reported in rats, mice and Syrian hamsters.

Demonstration by electron microscopy of viruses in cells found by light microscopy to contain inclusion bodies

Recently, a method was developed in this laboratory by means of which inclusion bodies found in cells during examination of histological sections might be processed for electron microscopy and by which the presence or absence of viruses in these bodies would be determined. The results of applying this method to the inclusion bodies of psittacosis, canine infectious hepatitis, equine viral rhinopneumonitis, bovine rabies and canine distemper are described. These demonstrate that definitive diagnosis can be established by this method.