1,721,072 research outputs found
Carbon Nanotubes and Their Composites for Flexible Electrochemical Biosensors
Full text linkFlexible biosensors play a crucial role for healthcare management and disease diagnosis. Electrochemical biosensors have attracted significant attention for wearable sensing applications owing to their numerous advantages, including high sensitivity and selectivity, inherent miniaturization and rapid response times. Challenges lie in the development of highly conductive and flexible electrodes that can be integrated with biorecognition components to engineer selective biosensor interfaces. Carbon nanotubes (CNTs) hold significant promise as materials for wearable flexible sensor fabrication. This review highlights recent strategies for fabricating conductive and flexible electrodes, whether in the form of films or fibers, based on CNTs and their composites. Additionally, the review explores emerging biosensing applications, including flexible sensors for the direct electrochemical detection of biomarkers, sensors functionalized with enzymes, antibodies, or DNA, and sensors interfaced w..
Electrochemically controlled assembly and logic gates operations of gold nanoparticle arrays
No full textThe reversible assembly of beta-cyclodextrin-functionalized gold NPs (beta-CD Au NPs) is studied on mixed self-assembled monolayer (SAM), formed by co-adsorption of redox-active ferrocenylalkylthiols and n-alkanethiols on gold surfaces. The surface coverage and spatial distribution of the beta-CD Au NPs monolayer on the gold substrate are tuned by the self-assembled monolayer composition. The binding and release of beta-CD Au NPs to and from the SAMs modified surface are followed by surface plasmon resonance (SPR) spectroscopy. The redox state of the tethered ferrocene in binary SAMs controls the formation of the supramolecular interaction between ferrocene moieties and beta-CD-capped Au NPs. As a result, the potential-induced uptake and release of beta-CD Au NPs to and from the surface is accomplished. The competitive binding of beta-CD Au NPs with guest molecules in solution shifted the equilibrium of the complexation decomplexation process involving the supramolecular interaction with the Fc-functionalized surface. The dual controlled assembly of beta-CD Au NPs on the surface enabled to use two stimuli as inputs for logic gate activation; the coupling between the localized surface plasmon, associated with the Au NP, and the surface plasmon wave, associated with the thin metal surface, is implemented as readout signal for "AND" logic gate operations
Transient Stiffness Patterning in Hydrogels Driven by Dissipative Mechanochemical Coupling
Full text linkLiving systems adapt to mechanical forces through a series of biochemical feedback loops and dissipative signal transduction mechanisms across multiple length scales. By contrast, synthetic materials are static, closed systems with minimal interaction with their surroundings and lack the ability to adapt to mechanical deformations. Here, a strategy that enables a hydrogel to adapt to mechanical forces through the temporal modulation of its stiffness properties is reported. It is demonstrated that force-induced bond rupture at the disulfide linkages of the hydrogel, coupled with their chemical reoxidation leads to dissipative, transient stiffness functions. The electrochemical generation of the oxidant as the output of a feedback loop triggered by an externally applied force provides high spatiotemporal control over the dissipative process, enabling the engineering of hydrogels with out-of-equilibrium stiffness patterns. Additionally, dose-controlled, spatiotemporal transient release of model protein payloads from the hydrogel is demonstrated. The proposed concept has the potential to enhance the autonomous and interactive functionalities of hydrogels, advancing their applications in the biomedical field and soft robotics
Electrochemical and surface plasmon resonance characterization of beta-cyclodextrin-based self-assembled monolayers and evaluation of their inclusion complexes with glucocorticoids
No full textThis paper describes the characterization of a self-assembled beta-cyclodextrin (beta-CD)-derivative monolayer (beta-CD-SAM) on a gold surface and the study of their inclusion complexes with glucocorticoids. To this aim the arrangement of a self-assembled beta-cyclodextrin-derivative monolayer on a gold surface was monitored in situ by means of surface plasmon resonance (SPR) spectroscopy and double-layer capacitance measurements. Film thickness and dielectric constant were evaluated for a monolayer of beta-CD using one-color-approach SPR. The selectivity of the beta-CD host surface was verified by using electroactive species permeable and impermeable in the beta-CD cavity. The redox probe was selected according to its capacity to permeate the beta-CD monolayer and its electrochemical behavior. In order to evaluate the feasibility of an inclusion complex between beta-CD-SAM with some steroids such as cortisol and cortisone, voltammetric experiments in the presence of the redox probes as molecules competitive with the steroids have been performed. The formation constant of the surface host-guest by beta-CD-SAM and the steroids under study was calculated
Cellulose-Based Functional Materials for Sensing
Full text linkThe growing bioeconomic demand for lightweight materials with combined sustainability, large-scale production, ease in functionalization and competitive mechanical properties has seen the revival of cellulose as a scaffold for several applications. In particular, due to its multifunctional features, cellulose has found application in sensor and biosensor fabrication. Nonetheless, the great variety of cellulose properties and formulations makes the choice of the best suited cellulose-based material for a specific sensing strategy a difficult task. This review offers a critical discussion and guide for the reader towards the understanding of which of the multiple cellulose derivatives and properties can be exploited for the optimal performance of the desired sensing device. We introduce the unique molecular structure, nanoarchitecture and main properties of cellulose and its derivatives. The different functionalization approaches for anchoring receptors on cellulose derivatives and the processing methodologies for fabricating cellulose-based sensors are explored. As far as the use and performance of cellulose-based functional materials in sensors is concerned, we discuss the recent advances of optical and electrochemical sensors and biosensors for biomedical and environmental monitoring
Selenium speciation in foods: Preliminary results on potatoes
No full textThe present paper deals with the speciation of selenium in potatoes (enriched or not in selenium). The study was carried out by using differential pulse cathodic stripping voltammetry (DPCSV) for quantifying selenium. Results obtained provide evidence that the selenium content in the protein fraction is rather independent from the selenium added to the plants during their growth. On the contrary, the amount of Se in the non-protein fraction (water and starch) in Se-enriched sample is significantly higher than in non-enriched one, suggesting that it is the main selenium-storing site. In this fraction the Se (VI)/Se(IV) ratio seems independent from selenium application but it may be related to the redox conditions. The accumulation of selenium in the nonprotein fraction is tentatively ascribed to the "Se-starch interaction" that should be able to modulate both the Se absorption into proteins and, possibly, its toxic effect for the plant itself. (c) 2006 Elsevier B.V. All rights reserved
Nanostructured materials based on the integration of ferrocenyl-tethered dendrimer and redox proteins on self-assembled monolayers: an efficient biosensor interface
No full textIn this paper we report the use of ferrocenyl-tethered dendrimer (Fc-D) as an electrode modifier supported by a self-assembled monolayer coated gold surface. The pretreatment of electrodes with Fc-D allows the covalent immobilization of glucose oxidase. The resulting integrated hybrid system provides electrical contact between the redox center of the enzyme and the electrode, and improves the overall bioelectrocatalyzed oxidation of glucose. Cyclic voltammetry combined with surface plasmon resonance (SPR) is used to investigate the redox-induced orientation changes of ferrocene-tethered dendrimers and the optimal electrical wiring of the enzyme, depending on the length of the alkyl chain of the ferrocene-tethered groups. The amount of substrate controls the steady-state concentration ratio of Fc/Fc(+) in the film composition. Therefore, the SPR spectrum of the film is controlled by the reversible change in the refractive index of the enzyme-integrated redox film. The proposed method demonstrates a new procedure for developing a stable amperometric redox enzyme-based sensor by designing a new nanostructured material that control the biosensing performance
Protein immobilization at gold-thiol surfaces and potential for biosensing
No full textSelf-assembled monolayers (SAMs) provide a convenient, flexible and simple system to tailor the interfacial properties of metals, metal oxides and semiconductors. Monomolecular films prepared by self-assembly are attractive for several exciting applications because of the unique possibility of making the selection of different types of terminal functional groups and as emerging tools for nanoscale observation of biological interactions. The tenability of SAMs as platforms for preparing biosurfaces is reviewed and critically discussed. The different immobilization approaches used for anchoring proteins to SAMs are considered as well as the nature of SAMs; particular emphasis is placed on the chemical specificity of protein attachment in view of preserving protein native structure necessary for its functionality. Regarding this aspect, particular attention is devoted to the relation between the immobilization process and the electrochemical response (i.e. electron transfer) of redox proteins, a field where SAMs have attracted remarkable attention as model systems for the design of electronic devices. Strategies for creating protein patterns on SAMs are also outlined, with an outlook on promising and challenging future directions for protein biochip research and applications
Electrochemically Stimulated pH Changes: A Route To Control Chemical Reactivity
No full textA bis-aniline-cross-linked Au nanoparticle (NP) composite is electrochemically prepared on a rough Pt film supported on a Au electrode The electrochemical oxidation of the bis-aniline units to the quinoid state releases protons to the electrolyte solution, while the reduction of the quinoid bridges results in the uptake of protons from the electrolyte. By the cyclic oxidation of the bridging units (E = 0.25 V vs SCE), and their reduction (E = -0 05 V vs SCE), the pH of the solution could be reversibly switched between the values 5 8 and 7 2, respectively The extent of the pH change is controlled by the number of electropolymerization cycles applied to synthesize the Au NP composite, demonstrating a ca 1 5 pH units change by a matrix synthesized using 100 electropolymerization cycles The pH changes are used to reversibly activate and deactivate a C-quadruplex (i-motif)-bridged Mg(2+)-dependent DNAzyme
Porous hydrogel scaffolds integrating Prussian Blue nanoparticles: A versatile strategy for electrochemical (bio)sensing
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