An interface comprising molecular wires and poly(ethylene glycol) spacer units self-assembled on carbon electrodes for studies of protein electrochemistry

Rapid nanomolar detection of Δ9-tetrahydrocannabinol in biofluids via electrochemical aptamer-based biosensor

BACKGROUND

The fabrication of sensors capable of achieving rapid, sensitive, and highly selective detection of target molecules in complex fluids is key to realizing their real-world applications. For example, there is an urgent need in drugged driving roadside screening scenarios to develop a method that can be used for rapid drug detection and that avoids interference from the matrix in the sample. How to minimize the interference of complex matrices in biofluids at the electrode interface is the key to improve the sensitivity of the sensor.

RESULTS

This work develops a facile and green method to prepare rough electrodes with a porous structure for constructing electrochemical aptamer-based (EAB) sensors for rapid, sensitive and accurate detection of Δ9-tetrahydrocannabinol (THC) in biofluids. The electroactive area of the rough electrode was 21 times of smooth electrode. And the antifouling performance of the rough electrode was much better than that of smooth electrode. Based on the unique advantages of the rough electrode, the developed EAB sensor achieves rapid nanomolar detection of THC in undiluted serum, undiluted urine and 50 % saliva with the detection limit of 5.0 nM, 10 nM and 10 nM, respectively. Moreover, our method possesses good reproducibility, accuracy and specificity.

SIGNIFICANCE

The porous structure can effectively reduce the non-specific adsorption and enhance the stability of the signal, while the larger active area can modify more aptamers, thus improving the sensitivity. The detection limits of the EAB sensor were lower than the cutoff concentration of THC in drugged driving and the measuring process was completed within 60 s after target addition, which makes the present sensors capable for real-world applications.

COF-Coated Microelectrode for Space-Confined Electrochemical Sensing of Dopamine in Parkinson's Disease Model Mouse Brain

Parkinson's disease (PD) is a progressive neurodegenerative disorder causing the loss of dopaminergic neurons in the substantia nigra and the drastic depletion of dopamine (DA) in the striatum; thus, DA can act as a marker for PD diagnosis and therapeutic evaluation. However, detecting DA in the brain is not easy because of its low concentration and difficulty in sampling. In this work, we report the fabrication of a covalent organic framework (COF)-modified carbon fiber microelectrode (cCFE) that enables the real-time detection of DA in the mouse brain thanks to the outstanding antibiofouling and antichemical fouling ability, excellent analytical selectivity, and sensitivity offered by the COF modification. In particular, the COF can inhibit the polymerization of DA on the electrode (namely, chemical fouling) by spatially confining the molecular conformation and electrochemical oxidation of DA. The cCFE can stably and continuously work in the mouse brain to detect DA and monitor the variation of its concentration. Furthermore, it was combined with levodopa administration to devise a closed-loop feedback mode for PD diagnosis and therapy, in which the cCFE real-time monitors the concentration of DA in the PD model mouse brain to instruct the dose and injection time of levodopa, allowing a customized medication to improve therapeutic efficacy and meanwhile avoid adverse side effects. This work demonstrates the fascinating properties of a COF in fabricating electrochemical sensors for in vivo bioanalysis. We believe that the COF with structural tunability and diversity will offer enormous promise for selective detection of neurotransmitters in the brain.

Advances in Biosensors for Continuous Glucose Monitoring Towards Wearables

Continuous glucose monitors (CGMs) for the non-invasive monitoring of diabetes are constantly being developed and improved. Although there are multiple biosensing platforms for monitoring glucose available on the market, there is still a strong need to enhance their precision, repeatability, wearability, and accessibility to end-users. Biosensing technologies are being increasingly explored that use different bodily fluids such as sweat and tear fluid, etc., that can be calibrated to and therefore used to measure blood glucose concentrations accurately. To improve the wearability of these devices, exploring different fluids as testing mediums is essential and opens the door to various implants and wearables that in turn have the potential to be less inhibiting to the wearer. Recent developments have surfaced in the form of contact lenses or mouthguards for instance. Challenges still present themselves in the form of sensitivity, especially at very high or low glucose concentrations, which is critical for a diabetic person to monitor. This review summarises advances in wearable glucose biosensors over the past 5 years, comparing the different types as well as the fluid they use to detect glucose, including the CGMs currently available on the market. Perspectives on the development of wearables for glucose biosensing are discussed.

Simultaneous Photografting of Two Organic Groups on a Gold Surface by using Arylazo Sulfones as Single Precursors

Arylazo sulfones have been exploited as photoactivatable substrates for the simultaneous photografting of both aryl and methanesulfonyl groups on a gold surface. The obtained samples have been characterized by different spectroscopic techniques including ellipsometry and electrochemistry, infrared reflection absorption, surface-enhanced Raman spectroscopy, XPS, and AFM. Grafting occurs through a simple N-S cleavage and not, as usually observed with aromatic precursors, by electron transfer.

Use of calixarenes bearing diazonium groups for the development of robust monolayers with unique tailored properties

Calixarene-based diazonium salts can be easily synthesized in a few steps. This review surveys recent examples that illustrate the key advantages of these highly reactive molecular platforms for surface modification.

Diazonium-Modified Screen-Printed Electrodes for Immunosensing Growth Hormone in Blood Samples

Altered growth hormone (GH) levels represent a major global health challenge that would benefit from advances in screening methods that are rapid and low cost. Here, we present a miniaturized immunosensor using disposable screen-printed carbon electrodes (SPCEs) for the detection of GH with high sensitivity. The diazonium-based linker layer was electrochemically deposited onto SPCE surfaces, and subsequently activated using covalent agents to immobilize monoclonal anti-GH antibodies as the sensing layer. The surface modifications were monitored using contact angle measurements and X-ray photoelectron spectroscopy (XPS). The dissociation constant, K_d, of the anti-GH antibodies was also determined as 1.44 (±0.15) using surface plasmon resonance (SPR). The immunosensor was able to detect GH in the picomolar range using a 20 µL sample volume in connection with electrochemical impedance spectroscopy (EIS). The selectivity of the SPCE-based immunosensors was also challenged with whole blood and serum samples collected at various development stages of rats, demonstrating the potential applicability for detection in biological samples. Our results demonstrated that SPCEs provided the development of low-cost and single-use electrochemical immunosensors in comparison with glassy carbon electrode (GCE)-based ones.

Whole Blood Redox Potential Correlates With Progressive Accumulation of Oxygen Debt and Acts as A Marker of Resuscitation in A Swine Hemorrhagic Shock Model

INTRODUCTION

Oxidation-reduction reactions involve electron exchanges that require optimal balance for proper cell function. This balance is measured via redox potential and reflects oxidative stress. Despite the critical role of oxidative stress in critical illness and injury, little is known regarding redox potential. We hypothesize redox potential measurements will correlate with accumulation of O2 debt produced by hemorrhage over time.

METHODS

Ten swine were studied using a polytrauma hemorrhagic shock model. Whole blood and plasma redox potential measures were obtained at defined stages of O2 debt (20 mL/kg, 40 mL/kg, 60 mL/kg, 80 mL/kg), and through resuscitation. Redox potential was determined by measuring open circuit potential using novel gold nanoporous electrodes with Ag/AgCl reference.

RESULTS

Whole blood redox potential showed negative change as O2 debt accumulated, exhibiting positive response during resuscitation, and correlated with O2 debt across all animals (P < 0.001). Redox potential changes throughout O2 debt accrual were significant compared with baseline (P≤0.05), and at end resuscitation compared with O2 debt 60 mL/kg (P = 0.05) and 80 mL/kg (P = 0.02). Whole blood redox potential measures also correlated with oxygen extraction ratio, ScvO2, and lactic acid, appearing very sensitive to acute changes. Plasma redox potential showed no correlation with O2 debt.

CONCLUSIONS

Whole blood redox potential demonstrates significant correlation to O2 debt at all stages in this model. These results set the stage for further study of redox potential as a direct measure of oxidative stress and potential clinical tool. Given redox potential plasma performance, these measures should be made in whole blood versus plasma.

Click Chemistry: A Versatile Method for Tuning the Composition of Mixed Organic Layers Obtained by Reduction of Diazonium Cations

Postfunctionalization of glassy carbon electrodes previously modified by reduction of 4-azidobenzenediazonium was exploited to conveniently synthesize controlled mixed organic layers. Huisgen 1,3-dipolar cycloaddition was used to anchor functional entities to azide platform. By this way, ((4-ethynylphenyl)carbamoyl)ferrocene (ϕ-Fc) was coimmobilized with a set of acetylene derivatives: 1-ethynyl-4-nitrobenzene (ϕ-NO₂), 4-ethynylaniline (ϕ-NH₂) or ethylnylbenzene (ϕ). The composition of the resulting organic layers was tuned by adjusting the acetylene derivatives ratio in the postfunctionalization binary solution. Electronic properties of the substituents beared by the aromatic rings were found to have a strong impact on the cycloaddition kinetics toward the confined azide moieties. From this study, rules to prepare finely tuned bifunctional organic layers can be anticipated.

Diruthenium(ii)-capped oligothienylethynyl bridged highly soluble organometallic wires exhibiting long-range electronic coupling

Organometallic molecular wires with π-conjugation along their molecular backbones are of considerable interest for application in molecular-scale electronics. In this regard, thienylethynyl-based π-conjugated oligomers of three, five and seven thienylethynyl units with -C[triple bond, length as m-dash]C-H termini have been successfully synthesized through stepwise Pd(0)/Cu(i)-catalyzed Sonogashira coupling. The corresponding highly soluble diruthenium(ii) diacetylide complexes (O1-Ru2, O3-Ru2, O5-Ru2 and O7-Ru2, respectively) have been prepared by the reaction of cis-Ru(dppe)2Cl2 and NaPF6 in DCM with the corresponding rigid rod-like thienylethynyl oligomers with one, three, five and seven thienylethynyl π-conjugated segments containing alkynyl termini (O1, O3, O5 and O7). These Ru(ii)-Cl capped diacetylide complexes have been further functionalized by incorporating a phenylacetynyl moiety to afford [Ru(ii)-C[triple bond, length as m-dash]C-Ph]-capped diacetylide organometallic wires (O1-Ru2-Ph, O3-Ru2-Ph, O5-Ru2-Ph and O7-Ru2-Ph). The photophysical properties of the highly soluble thienylethynyl-based oligomers and Ru(ii)-organometallic wires have been explored to understand their electronic properties. Electrochemical studies of the binuclear ruthenium(ii)-alkynyl complexes showed highly interesting results, revealing long-range electrochemical communication between the two remote Ru(ii) termini connected even with five and seven thienylethynyl units. DFT computational studies further support the long range electrochemical communication between the redox active metal termini through heavy participation of the thienylethynyl bridge in the corresponding mono-oxidized mixed valence species of the organometallic wire-like complexes.

In Situ Spectroelectrochemical Studies into the Formation and Stability of Robust Diazonium-Derived Interfaces on Gold Electrodes for the Immobilization of an Oxygen-Tolerant Hydrogenase

Surface-enhanced infrared absorption spectroscopy is used in situ to determine the electrochemical stability of organic interfaces deposited onto the surface of nanostructured, thin-film gold electrodes via the electrochemical reduction of diazonium salts. These interfaces are shown to exhibit a wide electrochemical stability window in both acetonitrile and phosphate buffer, far surpassing the stability window of thiol-derived self-assembled monolayers. Using the same in situ technique, the application of radical scavengers during the electrochemical reduction of diazonium salts is shown to moderate interface formation. Consequently, the heterogeneous charge-transfer resistance can be reduced sufficiently to enhance the direct electron transfer between an immobilized redox-active enzyme and the electrode. This was demonstrated for the oxygen-tolerant [NiFe] hydrogenase from the "Knallgas" bacterium Ralstonia eutropha by relating its electrochemical activity for hydrogen oxidation to the interface properties.

Integrated Affinity Biosensing Platforms on Screen-Printed Electrodes Electrografted with Diazonium Salts

Adequate selection of the electrode surface and the strategies for its modification to enable subsequent immobilization of biomolecules and/or nanomaterials integration play a major role in the performance of electrochemical affinity biosensors. Because of the simplicity, rapidity and versatility, electrografting using diazonium salt reduction is among the most currently used functionalization methods to provide the attachment of an organic layer to a conductive substrate. This particular chemistry has demonstrated to be a powerful tool to covalently immobilize in a stable and reproducible way a wide range of biomolecules or nanomaterials onto different electrode surfaces. Considering the great progress and interesting features arisen in the last years, this paper outlines the potential of diazonium chemistry to prepare single or multianalyte electrochemical affinity biosensors on screen-printed electrodes (SPEs) and points out the existing challenges and future directions in this field.

Grafting Commercial Surfactants (Brij, CiEj) and PEG to Electrodes via Aryldiazonium Salts

Grafting commercial surfactants appears to be a simple way to modify electrodes and conducting interfaces, avoiding the synthesis of complex organic molecules. A new surface functionalization route is presented to build surfactant coatings with monolayer thickness grafting molecules considered as nonreactive. A monolayer of -SO₂Cl functions (from a p-benzenesulfonyl chloride) was first electrografted. It showed a high reactivity toward weak nucleophiles commonly found on surfactant end-moieties such as hydroxyl groups (-OH), and it was used to covalently graft the following: (1) nonionic diblock oligomers (Brij or CiEj, C_xH_2x + (OCH₂CH₂)_nOH with x = 16 and n = 23 for Brij58, x = 16 and n = 10 for Brij C10, and x = 16 and n = 2 for Brij52); (2) poly(ethylene glycol) (PEG) short chains (PEO₉ for (OCH₂CH₂)_nOH with n = 9) and mixed formula. The surface modification due to these molecular coatings was investigated in terms of wetting properties and interfacial electrochemistry characteristics (charge transfer resistivity, capacity, and ions dynamics). Built on flat and transparent thin chromium films, Brij and PEO mixed coatings have been proven to be promising coatings for electrochemical biosensor application such as for stabilizing a partially tethered supported biomimetic membrane.

Advances on Aryldiazonium Salt Chemistry Based Interfacial Fabrication for Sensing Applications

Aryldiazonium salts as coupling agents for surface chemistry have evidenced their wide applications for the development of sensors. Combined with advances in nanomaterials, current trends in sensor science and a variety of particular advantages of aryldiazonium salt chemistry in sensing have driven the aryldiazonium salt-based sensing strategies to grow at an astonishing pace. This review focuses on the advances in the use of aryldiazonium salts for modifying interfaces in sensors and biosensors during the past decade. It will first summarize the current methods for modification of interfaces with aryldiazonium salts, and then discuss the sensing applications of aryldiazonium salts modified on different transducers (bulky solid electrodes, nanomaterials modified bulky solid electrodes, and nanoparticles). Finally, the challenges and perspectives that aryldiazonium salt chemistry is facing in sensing applications are critically discussed.

Synthesis and self-assembly of a D3h symmetric polycyclic aromatic hydrocarbon into a rigid 2D honeycomb network

C ₃ symmetric hexa-peri-hexabenzocoronene carboxylic acid assembles into a rigid 2D honeycomb network at a solid–liquid interface.

Multiplexed site-specific electrode functionalization for multitarget biosensors

Multitarget biosensors hold great promise to improve point-of-care diagnostics as they enable simultaneous detection of different biomolecular markers. Multiplexed detection of different markers, like genes, proteins, or a combination of both, propels advancement in numerous fields such as genomics, medical diagnosis and therapy monitoring. The functionalization of these biosensors, however, necessitates patterned immobilization of different bioreceptors, which remains challenging and time-consuming. We demonstrate a simple method for the patterned multiplexing of bioreceptors on a multi-electrode chip. By using the lithographically defined electrodes for surface functionalization, additional patterning steps become obsolete. Using the electrodes for self-aligned immobilization provides a spatial resolution that is limited by the electrode patterning process and that cannot be easily obtained by alternative dispensing or coating techniques. Via electrochemical reduction of diazonium salts combined with click chemistry, we achieved site-specific immobilization of two different ssDNA probes side by side on a single chip. This method was experimentally verified by cyclic voltammetry (CV), Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), and specific target recognition was visualized by fluorescence microscopy. The combination of the electroaddressability of electrografting with the chemoselectivity of click chemistry, offers a versatile platform for highly efficient site-specific functionalization of multitarget biosensors.

Strategies To Achieve Control over the Surface Ratio of Two Different Components on Modified Electrodes Using Aryldiazonium Salts

Controlling the composition of an interface is very important in tuning the chemical and physical properties of a surface in many applications including biosensors, biomaterials, and chemical catalysis. Frequently, this requires one molecular component to a minor component in a mixed layer. Such subtle control of composition has been difficult to achieve using aryldiazonium salts. Herein, aryldiazonium salts of carboxyphenyl (CP) and phenylphosphorylcholine (PPC), generated in situ from their corresponding anilines, are electrografted to form molecular platform that are available for further functionalization. These two components are chosen because CP provides a convenient functionality for further coupling of biorecognition species while PPC offers resistance to nonspecific adsorption of proteins to the surface. Mixed layers of CP and PPC were prepared by grafting them either simultaneously or consecutively. The latter strategy allows an interface to be developed in a controlled way where one component is at levels of less than 1% of the total layer.

Toward the Control of the Creation of Mixed Monolayers on Glassy Carbon Surfaces by Amine Oxidation

A versatile and simple methodology for the creation of mixed monolayers on glassy carbon (GC) surfaces was developed, using an osmium-bipyridyl complex and anthraquinone as model redox probes. The work consisted in the electrochemical grafting on GC of a mixture of mono-protected diamine linkers in varying ratios which, after attachment to the surface, allowed orthogonal deprotection. After optimisation of the deprotection conditions, it was possible to remove one of the protecting groups selectively, couple a suitable osmium complex and cap the residual free amines. The removal of the second protecting group allowed the coupling of anthraquinone. The characterisation of the resulting surfaces by cyclic voltammetry showed the variation of the surface coverage of the two redox centres in relation to the initial ratio of the linking amine in solution.

Advances in click chemistry for silica-based material construction

Click chemistry is undoubtedly the most powerful 1,3-dipolar cycloaddition reaction in organic synthesis.

Recent advances on developing 3rd generation enzyme electrode for biosensor applications

The electrochemical biosensor with enzyme as biorecognition element is traditionally pursued as an attractive research topic owing to their high commercial perspective in healthcare and environmental sectors. The research interest on the subject is sharply increased since the beginning of 21st century primarily, due to the concomitant increase in knowledge in the field of material science. The remarkable effects of many advance materials such as, conductive polymers and nanomaterials, were acknowledged in the developing efficient 3rd generation enzyme bioelectrodes which offer superior selectivity, sensitivity, reagent less detection, and label free fabrication of biosensors. The present review article compiles the major knowledge surfaced on the subject since its inception incorporating the key review and experimental papers published during the last decade which extensively cover the development on the redox enzyme based 3rd generation electrochemical biosensors. The tenet involved in the function of these direct electrochemistry based enzyme electrodes, their characterizations and various strategies reported so far for their development such as, nanofabrication, polymer based and reconstitution approaches are elucidated. In addition, the possible challenges and the future prospects in the development of efficient biosensors following this direct electrochemistry based principle are discussed. A comparative account on the design strategies and critical performance factors involved in the 3rd generation biosensors among some selected prominent works published on the subject during last decade have also been included in a tabular form for ready reference to the readers.

Electrografting of alkyl films at low driving force by diverting the reactivity of aryl radicals derived from diazonium salts

Alkyl and partial perfluoroalkyl groups are strongly attached to carbon surfaces through (i) the abstraction of the iodine atom from an iodoalkane by the sterically hindered 2,6-dimethylphenyl radical and (ii) the reaction of the ensuing alkyl radical with the carbon surface. Since the 2,6-dimethylphenyl radical is obtained at -0.25 V/Ag/AgCl by reducing the corresponding diazonium salt, the electrografting reaction is facilitated by ∼1.7 V by comparison with the direct electrografting of the iodo compounds. Layers of various thicknesses, including monolayers, are obtained by controlling the time duration of the electrolysis. The grafted films are characterized by electrochemistry, IR, XPS, ellipsometry, and water contact angles.