Alizarin Red S as an electrochemical indicator for saccharide recognition

Disposable electrochemical sensors based on reduced graphene oxide/polyaniline/poly(alizarin red S)-modified integrated carbon electrodes for the detection of ciprofloxacin in milk

An electrochemical sensor based on an electroactive nanocomposite was designed for the first time consisting of electrochemically reduced graphene oxide (ERGO), polyaniline (PANI), and poly(alizarin red S) (PARS) for ciprofloxacin (CIPF) detection. The ERGO/PANI/PARS-modified screen-printed carbon electrode (SPCE) was constructed through a three-step electrochemical protocol and characterized using FTIR, UV-visible spectroscopy, FESEM, CV, LSV, and EIS. The new electrochemical CIPF sensor demonstrated a low detection limit of 0.0021 μM, a broad linear range of 0.01 to 69.8 μM, a high sensitivity of 5.09 μA/μM/cm2, and reasonable selectivity and reproducibility. Moreover, the ERGO/PANI/PARS/SPCE was successfully utilized to determine CIPF in milk with good recoveries and relative standard deviation (< 5%), which were close to those with HPLC analysis.

Anthraquinone and its derivatives as sustainable materials for electrochemical applications - a joint experimental and theoretical investigation of the redox potential in solution

Anthraquinone (AQ) has long been identified as a highly promising lead structure for various applications in organic electronics. Considering the enormous number of possible substitution patterns of the AQ lead structure, with only a minority being commercially available, a systematic experimental screening of the associated electrochemical potentials represents a highly challenging and time consuming task, which can be greatly enhanced via suitable virtual pre-screening techniques. In this work the calculated electrochemical reduction potentials of pristine AQ and 12 hydroxy- or/and amino-substituted AQ derivatives in N,N-dimethylformamide have been correlated against newly measured experimental data. In addition to the calculations performed using density functional theory (DFT), the performance of different semi-empirical density functional tight binding (DFTB) approaches has been critically assessed. It was shown that the SCC DFTB/3ob parametrization in conjunction with the COSMO solvation model provides a highly adequate description of the electrochemical potentials also in the case of the two-fold reduced species. While the quality in the correlation against the experimental data proved to be slightly inferior compared to the employed DFT approach, the highly advantageous cost-accuracy ratio of the SCC DFTB/3ob/COSMO framework has important implications in the formulation of hierarchical screening strategies for materials associated with organic electronics. Based on the observed performance, the low-cost method provides sufficiently accurate results to execute efficient pre-screening protocols, which may then be followed by a DFT-based refinement of the best candidate structures to facilitate a systematic search for new, high-performance organic electronic materials.

Biomolecular interfaces based on self-assembly and self-recognition form biosensors capable of recording molecular binding and release

This research proposed to create the next generation of versatile electrochemical-based biosensors capable of monitoring target capture and release as dictated by molecular binding or unbinding. The biosensor integrates cellular machines (i.e., microtubules, structural elements of cells and kinesin molecular motors involved in cellular transport) as functional units; its assembly is based on molecular self-assembly and self-recognition. Our results demonstrate that the designed biosensor was capable of allowing detection of binding and unbinding events based on redox reactions at user-controlled electrode interfaces. The analysis also showed that the sensitivity of the designed biosensor or its ability to record such events could be user-controlled at any given time by adjusting the energy source that "fuels" the system.

Layer-by-Layer Assembly and Electrochemical Study of Alizarin Red S-Based Thin Films

Electroactive organic dyes incorporated in layer-by-layer (LbL) assemblies are of great interest for a variety of applications. In this paper, Alizarin Red S (ARS), an electroactive anthraquinone dye, is employed to construct LbL (BPEI/ARS)n films with branched poly(ethylene imine) (BPEI) as the complementary polymer. Unconventional LbL methods, including co-adsorption of ARS and poly(4-styrene sulfonate) (PSS) with BPEI to assemble (BPEI/(ARS+PSS))n, as well as pre-complexation of ARS with BPEI and further assembly with PSS to fabricate ((BPEI+ARS)/PSS)n, are designed for investigation and comparison. Film growth patterns, UV⁻Vis spectra and surface morphology of the three types of LbL assemblies are measured and compared to reveal the formation mechanism of the LbL films. Electrochemical properties including cyclic voltammetry and spectroelectrochemistry of (BPEI/ARS)120, (BPEI/(ARS+PSS))120 and ((BPEI+ARS)/PSS)120 films are studied, and the results show a slight color change due to the redox reaction of ARS. ((BPEI+ARS)/PSS)120 shows the best stability among the three samples. It is concluded that the manner of dye- incorporation has a great effect on the electrochemical properties of the resultant films.

Charge and Assembly Reversible Micelles Fueled by Intracellular ATP for Improved siRNA Transfection

Hydrophobic modification on polycations were commonly used to improve the stability and transfection efficiency of polyplexes. However, the improved stability often means undesired release of the encapsulated siRNA, limiting the application of cationic micelles for siRNA delivery. The current strategy of preparing bioresponsive micelles based on the cleavage of sensitive linkages between polycation and hydrophobic part was far from sufficient, owing to the siRNA binding of the separated polycations from micelles leading to the incomplete release of siRNA. In this study, we propose a new strategy by the combination of micelles disassembly and separated polycations charge reversal. FPBA (3-fluoro-4-carboxyphenylboronic acid) grafted PEI 1.8 k (polyethylenimine) as the polycations of PEI-FPBA and dopamine (with diol-containing moiety) conjugated with cholesterol as the hydrophobic part (Chol-Dopa). The PFCDM micelles was assembled by PEI-FPBA and Chol-Dopa, based on the FPBA-Dopa conjugation. The prepared PFCDM showed strong siRNA loading ability and superior stability in the presence of PBS or serum. Besides, the PFCDM exhibited excellent ATP sensibility. The intracellular ATP could effectively trigger the disassembly of micelles and charge reversal of PEI-FPBA, resulting in the burst release of siRNA in the cytosol. With the property of extracellular stability and intracellular instability, PFCDM displayed good performance on in vitro and in vivo luciferase silencing on 4T1 cells. It should also be noted that the assembly of low molecular weight PEI was relatively safe to cells compared with 25 k PEI. To sum up, the ATP-fueled assembly and charge reversible micelles gave examples for polyplexes to achieve better stability and on demand cargo release at the same time and shows potential to be used for in vitro and in vivo siRNA transfection.

Voltammetric Response of Alizarin Red S-Confined Film-Coated Electrodes to Diol and Polyol Compounds: Use of Phenylboronic Acid-Modified Poly(ethyleneimine) as Film Component

Alizarin red S (ARS) was confined in layer-by-layer (LbL) films composed of phenylboronic acid-modified poly(ethyleneimine) (PBA-PEI) and carboxymethylcellulose (CMC) to study the voltammetric response to diol and polyol compounds. The LbL film-coated gold (Au) electrode and quartz slide were immersed in an ARS solution to uptake ARS into the film. UV-visible absorption spectra of ARS-confined LbL film suggested that ARS formed boronate ester (ARS-PBS) in the film. The cyclic voltammetry of the ARS-confined LbL film-coated electrodes exhibited oxidation peaks at -0.50 and -0.62 V, which were ascribed to the oxidation reactions of ARS-PBS and free ARS, respectively, in the LbL film. The peak current at -0.62 V increased upon the addition of diol or polyol compounds such as L-dopa, glucose, and sorbitol into the solution, depending on the concentration, whereas the peak current at -0.50 V decreased. The results suggest a possible use of ARS-confined PBA-PEI/CMC LbL film-coated Au electrodes for the construction of voltammetric sensors for diol and polyol compounds.

U-Shaped and Surface Functionalized Polymer Optical Fiber Probe for Glucose Detection

In this work we show an optical fiber evanescent wave absorption probe for glucose detection in different physiological media. High selectivity is achieved by functionalizing the surface of an only-core poly(methyl methacrylate) (PMMA) polymer optical fiber with phenilboronic groups, and enhanced sensitivity by using a U-shaped geometry. Employing a supercontinuum light source and a high-resolution spectrometer, absorption measurements are performed in the broadband visible light spectrum. Experimental results suggest the feasibility of such a fiber probe as a low-cost and selective glucose detector.

Alizarin Red S-Confined Layer-By-Layer Films as Redox-Active Coatings on Electrodes for the Voltammetric Determination of L-Dopa

The preparation of redox-active coatings is a key step in fabricating electrochemical biosensors. To this goal, a variety of coating materials have been used in combination with redox-active compounds. In this study, alizarin red S (ARS) was confined in layer-by-layer (LbL) films composed of poly(ethyleneimine) (PEI) and carboxymethylcellulose (CMC) to study the redox properties. A gold (Au) disc electrode coated with PEI/CMC LbL film was immersed in an ARS solution to uptake ARS into the film. ARS was successfully confined in the LbL film through electrostatic interactions. The cyclic voltammogram (CV) of ARS-confined PEI/CMC film-coated electrodes thus prepared exhibited redox waves in the potential range from -0.5 to -0.7 V originating from 9,10-anthraquinone moiety in ARS, demonstrating that ARS preserves its redox activity in the LbL film. An additional oxidation peak appeared around -0.4 V in the CV recorded in the solution containing phenylboronic acid (PBA), due to the formation of a boronate ester of ARS (ARS-PBA) in the film. The oxidation peak current at -0.4 V decreased upon addition of 3,4-dihydroxyphenylalanine (L-dopa) to the solution. Thus, the results suggest a potential use of the ARS-confined PEI/CMC films for constructing voltammetric sensors for L-dopa.

Photochemical and computational studies of inclusion complexes between β-cyclodextrin and 1,2-dihydroxyanthraquinones

An inclusion complex is formed between 1,2-DHAQ and β-CD, which is confirmed by UV-visible, fluorescence and electrochemical studies, FT-IR, XRD, DSC, SEM, ¹H NMR and computational methods.

Saccharide Recognition Based on Self-Assembly of Amphiphilic Phenylboronic Acid Azoprobes

We designed amphiphilic phenylboronic acid azoprobes (B-Azo-Cn) and evaluated their saccharide recognition function in relation to the micelle formation changes of the self-assembled B-Azo-Cn. First, we evaluated B-Azo-C8 in a 1% methanol-99% water solution under basic conditions. The wavelength of maximum absorption in the ultraviolet-visible (UV-vis) spectra of B-Azo-C8 was shifted, and the solution showed a color change with the addition of saccharides. The morphology of B-Azo-C8 was evaluated using dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM) observations. B-Azo-C8 formed aggregates in the absence of saccharides and in the presence of glucose. In the presence of fructose, micelle-formed B-Azo-C8 was dispersed, indicating that B-Azo-C8 changed its dispersion state by recognizing fructose. The effect of alkyl chain length on the saccharide recognition ability was examined as well. B-Azo-C4 and B-Azo-C12 did not recognize saccharides in a 1% methanol-99% water solution under basic conditions, indicating that an appropriate alkyl chain length was required for recognizing saccharides. The control of the hydrophilic-lipophilic balance (HLB) was a key factor for saccharide recognition.

A quantitative appraisal of the binding interactions between an anionic dye, Alizarin Red S, and alkyloxypyridinium surfactants: a detailed micellization, spectroscopic and electrochemical study

The interactions of an anionic redox-active dye Alizarin Red S (ARS) with novel N-hydroxyethyl-3-alkyloxypyridinium surfactants 1-(2-hydroxyethyl)-3-(tetradecyloxy)pyridinium bromide, [HEC14OPyBr], and 1-(2-hydroxyethyl)-3-(hexadecyloxy)pyridinium bromide, [HEC16OPyBr], were investigated in an aqueous solution for the first time with an attempt to obtain comprehensive knowledge of oppositely charged dye-surfactant mixed systems. Different state-of-the-art techniques viz. conductivity, surface tension (ST), UV-visible spectroscopy, cyclic voltammetry (CV), linear sweep voltammetry (LSV), potentiometry, dynamic light scattering (DLS) and (1)H-NMR analysis have been employed. The presence of ARS decreases the critical micelle concentration (cmc) of alkyloxypyridinium surfactants as the ARS monomers behave as aromatic counterions. A combined analysis of the techniques revealed the existence of cation-π, π-π stacking, H-bonding, electrostatic and hydrophobic interactions among ARS and alkyloxypyridinium surfactants. A quantitative appraisal of the process of interaction among ARS and alkyloxypyridinium surfactants has been made in terms of various micellar, binding and electrochemical parameters evaluated using ST, UV-visible and voltammetric measurements. Also, the results extracted from (1)H-NMR and voltammetric measurements indicate that the catechol moiety of ARS is involved in the binding mechanism among ARS and alkyloxypyridinium surfactants.

Electrochemical and spectroscopic insights of interactions between alizarin red S and arsenite ions

ARS molecules are deprotonated in the presence of arsenite ions. The deprotonated form of ARS molecules show increase of charge transfer resistance and decrease of diffusion coefficient.

Recent Progress in Electrochemical HbA1c Sensors: A Review

This article reviews recent progress made in the development of electrochemical glycated hemoglobin (HbA1c) sensors for the diagnosis and management of diabetes mellitus. Electrochemical HbA1c sensors are divided into two categories based on the detection protocol of the sensors. The first type of sensor directly detects HbA1c by binding HbA1c on the surface of an electrode through bio-affinity of antibody and boronic acids, followed by an appropriate mode of signal transduction. In the second type of sensor, HbA1c is indirectly determined by detecting a digestion product of HbA1c, fructosyl valine (FV). Thus, the former sensors rely on the selective binding of HbA1c to the surface of the electrodes followed by electrochemical signaling in amperometric, voltammetric, impedometric, or potentiometric mode. Redox active markers, such as ferrocene derivatives and ferricyanide/ferrocyanide ions, are often used for electrochemical signaling. For the latter sensors, HbA1c must be digested in advance by proteolytic enzymes to produce the FV fragment. FV is electrochemically detected through catalytic oxidation by fructosyl amine oxidase or by selective binding to imprinted polymers. The performance characteristics of HbA1c sensors are discussed in relation to their use in the diagnosis and control of diabetic mellitus.

Functionalized vesicles based on amphiphilic boronic acids: a system for recognizing biologically important polyols

We report on a new approach for creating water-soluble functionalized vesicles employing N-alkyl-3-boronopyridinium triflates (alkyl = Me, C12H25, C16H33) as sensors for monosaccharides. The nanoaggregate properties were studied by means of DLS, TEM, high-resolution (1)H NMR, and the solvatochromic dyes Reichardt's betaine and Methyl Orange. The vesicles were shown to have 30-200 nm diameters depending on the amphiphile chain length. Diol binding to the vesicles was studied by steady-state fluorescence and UV-vis using Alizarin Red S as a probe in the solution at pH 7.4 in the presence and in the absence of D-glucose and D-fructose. Strong sensing ability of boronic acid functional moieties in the order D-fructose > D-glucose was demonstrated, and apparent binding constants were estimated.