Modified Gold Surface Research Articles

Bioreceptors’ immobilization by hydrogen bonding interactions and differential pulse voltammetry for completely label-free electrochemical biosensors

Label-free electrochemical biosensors show great potential for the development of point-of-care devices (POCDs) for environmental and clinical applications. These sensors operate with shorter analysis times and are more economic than the labelled ones. Here, four completely label-free biosensors without electron transfer mediators were developed for hepatitis B virus (HBV) detection. The approach consisted in (i) the modification of gold surfaces with cysteamine (CT) or cysteine (CS) linkers, (ii) the subsequent antibody (Ab) immobilization, either directly by hydrogen bonding (HB) interactions or by covalent bonds (CB) using additional reagents, and (iii) measuring the biosensor response by electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The electrode surfaces at each stage of the modification process were characterised by X-ray photo-electron spectroscopy (XPS) and atomic force microscopy (AFM). The combination of Ab immobilization by HB with the DPV analysis displayed improved repeatability, lower interference to serum matrix and similar limits of detection and quantification than the traditional biosensors that immobilize the Ab via CB and use EIS as readout technique. The Ab immobilization by HB is shown as a simple, efficient and low-cost alternative to CB ones, while DPV was faster and showed better performance than EIS. The CT-HB biosensor displayed the lowest limits of detection and quantification of 0.14 and 0.46 ng/mL, respectively, a 0.46–12.5 ng/mL linear analytical range, and 100% of recovery for 1/10 human serum media during HBV surface antigen detection by DPV. Even, it preserved the initial sensing capability after 7 days of its fabrication.Graphical abstract

Chiral recognition and amplification of melibiose based on (R)/(S)-phenylethylamine calix[4]arene modified gold surface

As a common substance in the human body, melibiose has a good effect on treating inflammation, and chiral selectively assembled behaviors often accompany this metabolic activity. Therefore, studies on melibiose's chiral selectively assembled behaviors arouse broad interest, making it better for us to understand similar bio-processes. Herein, we modified (R)/(S)-phenylethylamine calix[4]arenes onto the gold surface to analyze the chiral selective behaviors for melibiose. Contact angle and electrochemical experimental results showed that this functional surface modified with (S)-phenylethylamine calix[4]arene achieved selective adsorption of melibiose in the condition of pH = 7 based on the weak host–guest interaction. Furthermore, these functional surfaces have been realized by amplifying the weak selective interaction, and these chiral selective sensors have been constructed for the melibiose.

Surface-modified gold nanoparticles: A novel chemical probe for precise fluorescent detection of aluminium (Al3+) ions; investigating DFT insights and molecular logic gate behaviour

Trivalent metal cation fluorescence chemosensors are one of the most important areas of research because of their rarity. The necessity for easy-to-synthesize molecular chemosensors and to immobilize them on materials platform are enhancing continually. In this paper, we report the rapid sensing of Al3+ ion recognition by naphthalene derivative (N1) and tethered with gold nanoparticles (N1-AuNps). The cysteine-carrying naphthalene derivative is synthesized (Receptor-N1) and it forms a self-assembled monolayer on gold nanoparticles through the thiol moiety (N1-AuNPs). The structure of the synthesized receptor and the chemosensor assembled with AuNPs are characterized using spectroscopic and imaging techniques. On the gold nanoparticles, the surface-assembled compound highly selectively binds with Al3+ ion in the aqueous medium compared with a free receptor (N1). We present an improved colorimetric method that offers both high sensitivity and rapid detection for transition metal ions, specifically Al3+ ions. The determination of the binding stoichiometry and binding ratio between N1 / N1-AuNPs and Al3+ ion was achieved through the utilization of Jobs' plot and B-H plot which confirmed a 1:1 ratio. The binding phenomenon between N1-AuNPs and Al3+ ion has been ascertained to be predominantly according to the limited PET with CHEF impact technique. The N1-AuNPs chemosensor responds to H+ and Al3+ ions by demonstrating XOR molecular logic gate functionality and operating across a wide pH range. The nanoparticle-tethered chemosensor presents an effective system that can be employed in Al3+ ion sensing. The addition of Na2EDTA to the [N1-AuNPs - Al3+] complex solution caused a quenching of the fluorescence emission, which provides evidence of the reversible nature of the chemosensor. To gain further insights into the binding mode of Al3+ with N1-AuNPs, quantum mechanical investigations using density functional theory (TDDFT) have been conducted. We evaluated the effectiveness of our methodology for quantifying Al3+ ions in the water waste produced by significant industrial reactions.

Single-electron transfer reactions on surface-modified gold plasmons

Photoredox catalysis's relevance in organic synthesis research and innovation will increase in the coming decades. However, the processes rely almost exclusively on expensive noble metal complexes, most notably iridium complexes, to absorb light and transfer a single charge to a substrate or a catalyst to initiate cascade transformations. Light-triggered plasmon resonances generate a non-Fermi-Dirac energy distribution with many hot carriers that decay in ∼1 ps. Their ultrafast relaxation makes performing single electron transfer (SET) transformations challenging. Herein, a novel photosystem is proposed based on surface-modified gold nanoparticles (aka plasmon "molecularization"), which improved charge separation and, more importantly, enabled SET reactions, expanding the portfolio of photocatalysts available for photoredox catalysis. The photosystem was made into an electrode, permitting its use in photoelectrochemical arrangements that leverage electro- and photo-chemical approaches' benefits and chemical engineering solutions, helping the synthetic chemistry efforts towards greener synthesis and synthesis of more complex structures on a scale.

An application of carbohydrate polymers-based surface-modified gold nanoparticles for improved target delivery to liver cancer therapy - A systemic review

Gold nanoparticles have been broadly investigated as cancer diagnostic and therapeutic agents. Gold nanoparticles are a favorable drug delivery vehicle with their unique subcellular size and good biocompatibility. Chitosan, agarose, fucoidan, porphyran, carrageenan, ulvan and alginate are all examples of biologically active macromolecules. Since they are biocompatible, biodegradable, and irritant-free, they find extensive application in biomedical and macromolecules. The versatility of these compounds is enhanced because they are amenable to modification by functional groups like sulfation, acetylation, and carboxylation. In an eco-friendly preparation process, the biocompatibility and targeting of GNPs can be improved by functionalizing them with polysaccharides. This article provides an update on using carbohydrate-based GNPs in liver cancer treatment, imaging, and drug administration. Selective surface modification of several carbohydrate types and further biological uses of GNPs are focused on.

An Impedance-Based Immunosensor for the Detection of Ovalbumin in White Wine.

Food allergies are an exceptional response of the immune system caused by the ingestion of specific foods. The main foods responsible for allergic reactions are milk, eggs, seafood, soy, peanuts, tree nuts, wheat, and their derived products. Chicken egg ovalbumin (OVA), a common allergen molecule, is often used for the clarification process of wine. Traces of OVA remain in the wine during the fining process, and they can cause significant allergic reactions in sensitive consumers. Consequently, the European Food Safety Authority (EFSA) and the American Food and Drug Administration (FDA) have shown the risks for allergic people to assume allergenic foods and food ingredients, including eggs. Commonly, OVA detection requires sophisticated and time-consuming analytical techniques. Intending to develop a faster assay, we designed a proof-of-concept non-Faradaic impedimetric immunosensor for monitoring the presence of OVA in wine. Polyclonal antibodies anti-OVA were covalently immobilised onto an 11-mercaptoundecanoic-acid (11-MUA)-modified gold surface. The developed immunosensor was able to detect OVA in diluted white wine without the need for an external probe or any pre-treatment step with a sensitivity of 0.20 µg/mL, complying with the limit established by the resolution OIV/COMEX 502-2012 for the quantification of allergens in wine.

Potential Induced Protonation of the Second Coordination Sphere in a Hangman-type Iron Porphyrin Complex Promotes HER: Insights via in Situ Raman Spectroelectrochemistry.

The iron-based porphyrin complex containing a bispyridine-based hanging unit termed Py2XPFe was previously used as an effective catalyst for the reduction of protons to molecular hydrogen in solution. Here, the molecular compound was immobilized on a modified gold electrode surface and investigated by spectroelectrochemical methods under catalytic conditions. Immobilization of the Py2XPFe was facilitated using a pyridine-based amine linker molecule grafted to the gold electrode by electrochemical amine oxidation. The linker molecule denoted in this report as Pyr-1 allows for effective coordination of the iron porphyrin compound to the modified gold surface through axial coordination of the pyridine component to the Fe center. Resonance Raman spectroelectrochemistry was performed on the immobilized catalyst in pH 7 buffer at increasing cathodic potentials. This facilitates the electrochemical hydrogen evolution reaction (HER) while concurrently allowing for the observation of the v4, v3, and v2 porphyrin marker bands, which are sensitive to oxidation and spin state changes at the metal center. The observed changes in these bands at decreasing potential indicate that the immobilized Py2XPFe exists in the formal high-spin FeIII state before being reduced to the low-spin FeII state resulting from axial interaction with the linker moiety. This FeII state likely acts as the precatalyst for the HER reaction. Surfaced enhanced Raman spectroelectrochemistry was also conducted on the system as the gold electrode provides a sufficient surface enhancement effect so as to observe the bonding nature of the pyridine substituents within the second coordination sphere. As the potential is lowered cathodically, the pyridine ring breathing modes at 999 cm-1 are shown to increase in intensity due to protonation, which reach an intensity saturated limit whereat HER is conducted. This suggests that in pH 7 buffer, the increase in cathodic potentials facilitates protonation of the pyridine-based second coordination sphere. The extent to which protonation occurs can be viewed as a function of decreasing potential due to an increase in proton flux at the immobilized catalyst which, at the required onset potential for catalysis, aids in the reduction of protons to molecular hydrogen.

A Quartz Crystal Microbalance (QCM) Study on the Formation of Aqueous κ-Carrageenan-Chitosan Composite Bilayers with NaCl and Graphene Oxide

Biomaterials and thin biofilms play a fundamental role in the medical, food and pharmaceutical industries. The Quartz crystal microbalance (QCM) measurement technique is one of the attractive techniques which have been used for monitoring the thin-film formation process. In the current work described here, κ-carrageenan and chitosan solutions were used for the layer-by-layer (LBL) deposition of polyelectrolyte multilayers (PEMs) on the gold surface of a 5 MHz AT-cut (thickness-shear mode) quartz crystal in a flow module. A sensitive QCM system was designed to detect 0.1 Hz differences in the resonance frequency (Δf) and 10−7 changes in the energy dissipation (ΔD) values, which are the measures of the deposited mass and the film rigidity, respectively. Negatively charged carrageenan and positively charged chitosan biomolecules in the solutions were used to build up sequential and very thin bilayers on the modified gold surface. The effects of NaCl and graphene oxide (GO) addition on the mass of the deposited films were also investigated. Intermolecular interactions between the biopolymer chains, Na+ cations and GO sheets were explained by interactions between molecules, such as electrostatic forces and hydrogen bondings.

Investigations of stable surface-modified gold nanofluids optical filters based on optical optimization for photovoltaic/thermal systems

Nanofluid filters have become increasingly popular for solar photovoltaic/thermal (PV/T) systems due to their tunable optical and thermal properties, especially for some plasmonic nanofluids. However, towards optimizing the characteristics of the plasmonic nanofluids filters, by identifying the best nanofluid parameters and improving their long-term dispersion stability, more researches need to be conducted. In this work, the effects of nanoparticles concentration, optical thickness and nanoparticle size on performance of Au nanofluids filtered PV/T systems are investigated theoretically. The PV/T systems can obtain optimal merit function (MF) of 1.367 and 1.357 for Au/water nanofluid and Au/ethylene glycol (EG) nanofluid, respectively. Then, surface-modified Au nanoparticles capped with polyethylene glycol (PEG) or polyvinylpyrrolidone (PVP) polymers are prepared and dispersed in water and EG, respectively. The stability of the stabilizer coated Au nanofluids upon long-term ambient storage, continuous heating, cyclic flowing and solar radiation is discussed. Au + PVP/EG nanofluids exhibit more excellent thermal stability than that of Au + PVP/water. To study the effectiveness of the optimal Au + PVP/EG nanofluids filtered PV/T system, indoor flowing experiments are conducted. The optimal MF of 1.95 and exergy efficiency of 13.98% is achieved filtered by Au + PVP/EG nanofluid with concentration of 29.2 ppm when mass flow rate is 2 mL/min.

Methylthiophenyl- and Methylthiobiphenyl-Substituted A2B CoIIIcorroles: Modulating Electrocatalyzed Hydrogen Evolution Reactions on Surface-Modified Gold Electrodes

Four A2B-type CoIIIcorroles (2a-2d) with electron-donating/withdrawing substituents at the A2 meso-aryl substituents and a 4-(methylthio)phenyl ring at the B position have been synthesized and characterized, along with a series of meso-extended CoIIIcorroles (4a-4c) with 4'-(methylthio)biphenyl moieties. The electronic structures and structure-property relationships of the dyes have been analyzed by comparing their redox and optical properties to trends predicted in density functional theory calculations. Au electrodes surface-modified with 2a-2d and 4a-4c are highly efficient catalysts for electrocatalyzed hydrogen evolution reactions, and the electrocatalytic properties can be readily modulated by fine-tuning the electronic structure of the CoIIIcorrole and the distance between the "Au-S" bond and CoIII center.

Surface modification of gold by carbazole dendrimers for improved carbon dioxide electroreduction.

Four types of carbazole dendrimers were applied as modification molecules of Au surfaces to improve carbon dioxide electroreduction. The reduction properties depended on the molecular structures: the highest activity and selectivity to CO was achieved by 9-phenylcarbazole, probably caused by the charge transfer from the molecule to Au.

Development of a quartz crystal microbalance-based immunosensor for the early detection of mesothelin in cancer

A robust real-time flow injection assay using Quartz Crystal Microbalance (QCM) biosensor has been developed for the detection of mesothelin, an antigen expressed on various malignant tumors including mesothelioma and ovarian cancers. A QCM sensor chip functionalized with self-assembled monolayer of cysteamine used to fabricate a sensitive immunosensor. Mesothelin specific antibody was immobilized on cysteamine modified gold surface of quartz crystal using N-ethyl-N’-(3-dimethylaminopropyl) carbodiimide and N-hydroxy succinimide coupling. Further, ethanolamine was used as a blocking reagent to prevent the non-specific adsorption on antibody functionalized gold surface. Various concentrations of mesothelin was tested and the resonant frequency variation of the crystal was observed by a quartz crystal microbalance until a stable response is obtained. A good correlation between the frequency changes and concentration of mesothelin tested was observed and the QCM biosensor detects mesothelin in the linear range of 100pg/mLto 50 ng/mL. Thus, QCM assay could be a promising technique for early diagnosis of mesothelioma, ovarian and pancreatic adenocarcinoma.

CRGD-targeted gold-based nanoparticles overcome EGFR-TKI resistance of NSCLC via low-temperature photothermal therapy combined with sonodynamic therapy.

Epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) is a first-line targeted drug for the treatment of advanced non-small cell lung cancer (NSCLC) in clinical practice, but EGFR-TKI-acquired resistance limits its therapeutic effect. To address this challenge, a novel multifunctional gold-based targeted nanoparticle-based drug delivery system is fabricated. The gold-based nanoparticle is loaded with the EGFR-TKI (gefitinib) and IR780, and the surface-modified gold nanoshell layer has a photothermal effect for thermally triggered drug release. Finally, the unique binding of cyclic arginine-glycine-aspartic acid (cRGD) to the αvβ3 receptor ensured that the nanoparticle (cRGD-GIPG) targeted transport into drug-resistant NSCLC cells was functional. Due to the sonodynamic properties of IR780, ultrasound (US) irradiation promoted reactive oxygen species (ROS) generation, while low-temperature photothermal therapy (PTT) not only promoted the release of drug, but also further enhanced the cytotoxic effects of ROS. In turn, it blocked the activation of TGF-β/PDLIM5/SMAD resistance pathway and induced apoptosis of drug-resistant cells through mitochondrial apoptosis, enabling the treatment of EGFR-TKI-resistant NSCLC. The low-temperature PTT combined with sonodynamic therapy (SDT) by cRGD-GIPG thus shows potent anticancer activity against EGFR-TKI-resistant NSCLC cells in vitro and in vivo. The present work provides a valuable strategy for highly targeted and EGFR-TKI-resistant reversal therapy in NSCLC.

Astatine-211-Labeled Gold Nanoparticles for Targeted Alpha-Particle Therapy via Intravenous Injection.

Alpha-particle radiotherapy has gained considerable attention owing to its potent anti-cancer effect. 211At, with a relatively short half-life of 7.2 h, emits an alpha particle within a few cell diameters with high kinetic energy, which damages cancer cells with high biological effectiveness. In this study, we investigated the intravenous injection of 211At-labeled gold nanoparticles (AuNPs) for targeted alpha-particle therapy (TAT). Different kinds of surface-modified gold nanoparticles can be labeled with 211At in high radiochemical yield in 5 min, and no purification is necessary. The in vivo biodistribution results showed the accumulation of 5 nm 211At-AuNPs@mPEG at 2.25% injection dose per gram (% ID/g) in tumors within 3 h via the enhanced permeability and retention (EPR) effect. Additionally, we observed a long retention time in tumor tissues within 24 h. This is the first study to demonstrate the anti-tumor efficacy of 5 nm 211At-AuNPs@mPEG that can significantly suppress tumor growth in a pancreatic cancer model via intravenous administration. AuNPs are satisfactory carriers for 211At delivery, due to simple and efficient synthesis processes and high stability. The intravenous administration of 5 nm 211At-AuNPs@mPEG has a significant anti-tumor effect. This study provides a new framework for designing nanoparticles suitable for targeted alpha-particle therapy via intravenous injection.

Following the Aggregation of Human Prion Protein on Heparin Functionalized Gold Surface in Real Time.

The aggregation of the prion protein (PrP) plays a key role in the development of prion diseases and is believed to be an autocatalytic process with a very high kinetic barrier. Intensive studies have focused on overcoming the kinetic barriers under extremely nonphysiological in vitro conditions by altering the pH of PrP solution on solid surfaces, such as gold, mica, and a lipid bilayer. Importantly, sulfated glycosaminoglycans (GAGs), including heparin, were found to be associated with PrP misfolding and aggregation, suggesting GAGs have catalytic roles in PrP aggregation processes. However, the exact role and details of GAGs in the PrP aggregation are not clear and need a thorough perusal. Here, we investigate the PrP aggregation process on a heparin functionalized gold surface by in situ, real-time monitoring of the atomic scale details of the whole aggregation process by single molecule atomic force microscopy (AFM), combining simultaneous topographic and recognition (TREC) imaging and single molecule force spectroscopy (SMFS). We observed the whole aggregation process for full-length human recombinant PrP (23-231) aggregation on the heparin modified gold surface, from the formation of oligomers, to the assembly of protofibrils and short fibers, and the formation of elongated mature fibers. Heparin is found to promote the PrP aggregation by facilitating the formation of oligomers during the early nucleation stage.

End to end aligned surface-modified gold nanorod for the detection of calcium

• Surface modification of the gold nanorod resulted in the end to alignment. • The calcium was detected in blood serum. • A paper-based strip was fabricated for the detection calcium. • The limit of detection of the sensor was found to be 14 nm. Point-of-care diagnostics devices are the next generation biosensors for the early detection of diseases. Nanotechnology can offer greater promise in this field. An end-to-end aligned gold nanorod is used as a sensor for the detection of calcium. The developed sensor is validated for calcium sensing in blood serum. The limit of detection of the developed sensor is 14 nM. Paper-based strips are fabricated using the developed sensor for the detection of calcium.

Developmental Toxicity of Surface-Modified Gold Nanorods in the Zebrafish Model.

Background: nanotechnology is one of the fastest-growing areas, and it is expected to have a substantial economic and social impact in the upcoming years. Gold particles (AuNPs) offer an opportunity for wide-ranging applications in diverse fields such as biomedicine, catalysis, and electronics, making them the focus of great attention and in parallel necessitating a thorough evaluation of their risk for humans and ecosystems. Accordingly, this study aims to evaluate the acute and developmental toxicity of surface-modified gold nanorods (AuNRs), on zebrafish (Danio rerio) early life stages. Methods: in this study, zebrafish embryos were exposed to surface-modified AuNRs at concentrations ranging from 1 to 20 μg/mL. Lethality and developmental endpoints such as hatching, tail flicking, and developmental delays were assessed until 96 h post-fertilization (hpf). Results: we found that AuNR treatment decreases the survival rate in embryos in a dose-dependent manner. Our data showed that AuNRs caused mortality with a calculated LC50 of EC50,24hpf of AuNRs being 9.1 μg/mL, while a higher concentration of AuNRs was revealed to elicit developmental abnormalities. Moreover, exposure to high concentrations of the nanorods significantly decreased locomotion compared to untreated embryos and caused a decrease in all tested parameters for cardiac output and blood flow analyses, leading to significantly elevated expression levels of cardiac failure markers ANP/NPPA and BNP/NPPB. Conclusions: our results revealed that AuNR treatment at the EC50 induces apoptosis significantly through the P53, BAX/BCL-2, and CASPASE pathways as a suggested mechanism of action and toxicity modality.

Determination of the Highly Sensitive Carboxyl-Graphene Oxide-Based Planar Optical Waveguide Localized Surface Plasmon Resonance Biosensor.

This study develops a highly sensitive and low-cost carboxyl-graphene-oxide-based planar optical waveguide localized surface plasmon resonance biosensor (GO-OW LSPR biosensor), a system based on measuring light intensity changes. The structure of the sensing chip comprises an optical waveguide (OW)-slide glass and microfluidic-poly (methyl methacrylate) (PMMA) substrate, and the OW-slide glass surface-modified gold nanoparticle (AuNP) combined with graphene oxide (GO). As the GO has an abundant carboxyl group (–COOH), the number of capture molecules can be increased. The refractive index sensing system uses silver-coated reflective film to compare the refractive index sensitivity of the GO-OW LSPR biosensor to increase the refractive index sensitivity. The result shows that the signal variation of the system with the silver-coated reflective film is 1.57 times that of the system without the silver-coated reflective film. The refractive index sensitivity is 5.48 RIU−1 and the sensor resolution is 2.52 ± 0.23 × 10−6 RIU. The biochemical sensing experiment performs immunoglobulin G (IgG) and streptavidin detection. The limits of detection of the sensor for IgG and streptavidin are calculated to be 23.41 ± 1.54 pg/mL and 5.18 ± 0.50 pg/mL, respectively. The coefficient of variation (CV) of the repeatability experiment (sample numbers = 3) is smaller than 10.6%. In addition, the affinity constants of the sensor for anti-IgG/IgG and biotin/streptavidin are estimated to be 1.06 × 107 M−1 and 7.30 × 109 M−1, respectively. The result shows that the GO-OW LSPR biosensor has good repeatability and very low detection sensitivity. It can be used for detecting low concentrations or small biomolecules in the future.

In-sera selectivity detection of catecholamine neurotransmitters using covalent composite of cobalt phthalocyanine and aminated graphene quantum dots

Here, we constructed an electrochemical sensor for the detection of catecholamine neurotransmitters based on covalent composite of cobalt tetra-(3-carboxyphenoxy) phthalocyanine (CoTCPhOPc) onto aminated graphene quantum dots (AmGQDs). The electrochemical behaviour of the covalent composite modified gold surface was studied using cyclic voltammetry, differential pulse voltammetry, square wave voltammetry and electrochemical impedance spectroscopy. The electrochemical sensor fabricated using gold surface with AmGQD-CoTCPhOPc exhibited enhanced electrical conductivity. The fabricated electrochemical sensor displayed excellent analytical performance towards the detection of dopamine (DA), norepinephrine (NOR) and epinephrine (EP). The analytical parameters were linear within the concentration range of 1.0 to 50 μM with detection limits of 0.20 µM (DA), 0.45 µM (NOR), and 0.23 µM (EP) using S/N = 3. Furthermore, the fabricated electrochemical sensor exhibited good ability to suppress the background current due to ascorbic acid (AA), a major interferent during detection of DA, EP and NOR analytes. More importantly, the developed covalent electrochemical sensor was successfully utilized for the detection of catecholamine neurotransmitters in newborn calf serum samples with high recovery percentages.

Expression, purification, characterization and direct electrochemistry of two HiPIPs from Acidithiobacillus caldus SM-1

High-potential iron-sulfur proteins (HiPIPs) from extremely acidophilic chemolithotrophic non-photosynthetic Acidithiobacillus commonly play a crucial role in ferrous or sulfurous biooxidation. Acidithiobacillus exhibit important industrial applications for bioleaching valuable metals from sulfide ores. In this study, two HiPIP genes from thermophilic Acidithiobacillus caldus SM-1 were cloned and successfully expressed, and their proteins were purified. The proteins displayed a brownish color with an optical absorbance peak at approximately 385 nm and an electronic paramagnetic resonance (EPR) g value of approximately 2.01, which confirmed that the iron-sulfur cluster was correctly inserted into the active site when the proteins were generated in E. coli. The proteins were more thermostable than HiPIPs from mesophilic Acidithiobacillus. The direct electron transfer (DET) between HiPIPs and electrode was achieved by the 2-mercaptopyrimidine (MP) surface-modified gold electrodes; the redox potentials of the HiPIP1 and HiPIP2 measured by cyclic voltammetry were approximately 304.5 mV and 400.5 mV, respectively. The electron transfer rate constant was estimated to be 0.75 s−1 and 0.66 s−1, respectively. The MP/Au electrode and Au electrode showed consistent differences in heterogeneous electron transfer rates and electron transfer resistances. Bioinformatics and molecular simulations further explained the direct electron transfer between the proteins and surface-modified electrode.