Microneedle-based biosensor for minimally-invasive lactate detection

Here we report the first mediated microneedles-based biosensor for minimally invasive continuous sensing of lactate in the dermal interstitial fluid (ISF). To further demonstrate the capability of microneedle arrays as second generation biosensors we have functionalized gold microneedles with nanocarbons at which mediated electron transfer of lactate oxidase takes place. In particular the gold surface of the microneedles electrode has been modified in 3 subsequent steps: i) electrodeposition of Au-multiwalled carbon nanotubes (MWCNTs); ii) electropolymerization of the mediator, methylene blue (MB); iii) immobilization of the enzyme lactate oxidase (LOX) by drop-casting procedure. The resulting microneedle-based LOX biosensor displays an interference-free lactate detection without compromising its sensitivity, stability, selectivity and response time. The performance of the microneedle array, second generation biosensor for lactate detection was assessed in artificial interstitial fluid and in human serum, both spiked with lactate. The results reveal that the new mi- croneedles lactate sensor holds interesting promise for the development of a real-time monitoring device to be used in sport medicine and clinical care

Surface plasmon resonance assay for label-free and selective detection of hiv-1 p24 protein

The early detection of the human immunodeficiency virus (HIV) is of paramount importance to achieve efficient therapeutic treatment and limit the disease spreading. In this perspective, the assessment of biosensing assay for the HIV-1 p24 capsid protein plays a pivotal role in the timely and selective detection of HIV infections. In this study, multi-parameter-SPR has been used to develop a reliable and label-free detection method for HIV-1 p24 protein. Remarkably, both physical and chemical immobilization of mouse monoclonal antibodies against HIV-1 p24 on the SPR gold detecting surface have been characterized for the first time. The two immobilization techniques returned a capturing antibody surface coverage as high as (7.5 ± 0.3) × 1011 molecule/cm2 and (2.4 ± 0.6) × 1011 molecule/cm2, respectively. However, the covalent binding of the capturing antibodies through a mixed self-assembled monolayer (SAM) of alkanethiols led to a doubling of the p24 binding signal. Moreover, from the modeling of the dose-response curve, an equilibrium dissociation constant KD of 5.30 × 10−9 M was computed for the assay performed on the SAM modified surface compared to a much larger KD of 7.46 × 10−5 M extracted for the physisorbed antibodies. The chemically modified system was also characterized in terms of sensitivity and selectivity, reaching a limit of detection of (4.1 ± 0.5) nM and an unprecedented selectivity ratio of 0.02

Minimally Invasive Glucose Monitoring Using a Highly Porous Gold Microneedles-Based Biosensor: Characterization and Application in Artificial Interstitial Fluid

In this paper, we present the first highly porous gold (h-PG) microneedles-based second-generation biosensor for minimally invasive monitoring of glucose in artificial interstitial fluid (ISF). A highly porous microneedles-based electrode was prepared by a simple electrochemical self-templating method that involves two steps, gold electrodeposition and hydrogen bubbling at the electrode, which were realized by applying a potential of −2 V versus a saturated calomel electrode (SCE). The highly porous gold surface of the microneedles was modified by immobilization of 6-(ferrocenyl)hexanethiol (FcSH) as a redox mediator and subsequently by immobilization of a flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH) enzyme using a drop-casting method. The microneedles-based FcSH/FAD-GDH biosensor allows for the detection of glucose in artificial interstitial fluid with an extended linear range (0.1–10 mM), high sensitivity (50.86 µA cm−2 mM−1), stability (20% signal loss after 30 days), selectivity (only ascorbic acid showed a response about 10% of glucose signal), and a short response time (3 s). These properties were favourably compared to other microneedles-based glucose biosensors reported in the literature. Finally, the microneedle-arrays-based second-generation biosensor for glucose detection was tested in artificial interstitial fluid opportunely spiked with different concentrations of glucose (simulating healthy physiological conditions while fasting and after lunch) and by placing the electrode into a simulated chitosan/agarose hydrogel skin model embedded in the artificial ISF (continuous glucose monitoring). The obtained current signals had a lag-time of about 2 min compared to the experiments in solution, but they fit perfectly into the linearity range of the biosensor (0.1–10 mM). These promising results show that the proposed h-PG microneedles-based sensor could be used as a wearable, disposable, user-friendly, and automated diagnostic tool for diabetes patients

Worst-case analysis of heap allocations

Abstract. In object oriented languages, dynamic memory allocation is a fundamental concept. When using such a language in hard real-time systems, it becomes important to bound both the worst-case execution time and the worst-case memory consumption. In this paper, we present an analysis to determine the worst-case heap allocations of tasks. The analysis builds upon techniques that are well established for worst-case execution time analysis. The difference is that the cost function is not the execution time of instructions in clock cycles, but the allocation in bytes. In contrast to worst-case execution time analysis, worst-case heap allocation analysis is not processor dependent. However, the cost function depends on the object layout of the runtime system. The analysis is evaluated with several real-time benchmarks to establish the usefulness of the analysis, and to compare the memory consumption of different object layouts.

Mobile Resource Guarantees and Policies

Abstract. This paper introduces notions of resource policy for mobile code to be run on smart devices, to integrate with the proof-carrying code architecture of the Mobile Resource Guarantees (MRG) project. Two forms of policy are used: guaranteed policies which come with proofs and target policies which describe limits of the device. A guaranteed policy is expressed as a function of a methods input sizes, which determines a bound on consumption of some resource. A target policy is defined by a constant bound and input constraints for a method. A recipient of mobile code chooses whether to run methods by comparing between a guaranteed policy and the target policy. Since delivered code may use methods implemented on the target machine, guaranteed policies may also be provided by the platform; they appear symbolically as assumptions in delivered proofs. Guaranteed policies entail proof obligations that must be established from the proof certificate. Before proof, a policy checker ensures that the guaranteed policy refines the target policy; our policy format ensures that this step is tractable and does not require proof. Delivering policies thus mediates between arbitrary target requirements and the desirability to package code and certificate only once.

Transdermal Microneedle Array-Based Biosensor for Real Time Simultaneous Lactate and Glucose Monitoring

Microneedle arrays for minimally invasive continuous sensing in the dermal interstitial fluid (ISF) have been demonstrated in both amperometric [1,2] and potentiometric [3] modes, however there are no publication where microneedle arrays have been shown to function as second generation biosensors [4]. […

Porous gold: A new frontier for enzyme-based electrodes

Porous gold (PG) layers modified electrodes have emerged as valuable enzyme support to realize multiple enzyme-based bioelectrochemical devices like biosensors, enzymatic fuel cells (EFCs), smart drug delivery devices triggered by enzyme catalyzed reactions, etc. PG films can be synthesized by using different methods such as dealloying, electrochemical (e.g., templated electrochemical deposition, self-templated electrochemical deposition, etc.) self-assembly and sputter deposition. This review aims to summarize the recent findings about PG synthesis and electrosynthesis, its characterization and application for enzyme-based electrodes used for biosensors and enzymatic fuel cells (EFCs) development

Bioelectrocatalysis at carbon nanotubes

This paper summarizes several examples of enzyme immobilization and bioelectrocatalysis at carbon nanotubes (CNTs). CNTs offer substantial improvements on the overall performance of amperometric enzyme electrodes mainly due to their unique structural, mechanical and electronic properties such as metallic, semi-conducting and superconducting electron transport. Unfortunately, their water insolubility restrains the kick-off in some particular fields. However, the chemical functionalization of CNTs, non-covalent and covalent, attracted a remarkable interest over the past several decades boosting the development of electrochemical biosensors and enzymatic fuel cells (EFCs) based on two different types of communications: mediated electron transfer (MET)-type, where the use of redox mediators, small electroactive molecules (freely diffusing or bound to side chains of flexible redox polymers), which are able to shuttle the electrons between the enzyme active site and the electrode (second electron transfer generation system); direct electron transfer (DET)-type between the redox group of the enzyme and the electrode surface (third electron transfer generation system)

Enzyme based amperometric biosensors

Current research on enzyme based electrochemical biosensors deals essentially with the same target analytes as was at focus in the early days of biosensor research, that is those within the clinical/medical, food/agriculture, and environmental fields [1•–13]. However, there has been substantial progress through the years and progress continues, as resumed in Figure 1A. One of the major differences is that (bio)electrochemists finally seem to start to understand what kind of molecules they deal with, that is with biological molecules and vice versa, biochemists, (micro)biologists start to become interested in (bio)electrochemistry. This is clearly shown for example in the recent very intense research on biofuel cells [14–26] and lately also on biosupercapacitors [27] that has absolutely had a great influence on current research on enzyme based biosensors and bioelectrochemistry as a whole

Fuel Cells and Biofuel Cells: From Past to Perspectives

This review aims at summarizing the history and state-of-the-art in the areas of fuel and biofuel cells. The paper is addressed to a broad audience including experts and particularly to newcomers and students. Some parts of the review, particularly about fuel cells of different kinds, are rather general and mostly addressed to students, however, sections related to biofuel cells are more specialized and will be interesting for researchers working in this novel and challenging area. Many aspects discussed in the article represent personal opinions of the authors. The article is aimed at providing interesting and easy for reading material representing more concepts than specific experimental data. If the readers get excited about the topic, the authors’ goals will be satisfied