Indium Tin Oxide Surface Research Articles

Electrochemical detection and analysis of tumor-derived extracellular vesicles to evaluate malignancy of pancreatic cystic neoplasm using integrated microfluidic device

Tumor-derived extracellular vesicles (tdEVs) are one of the most promising biomarkers for liquid biopsy-based cancer diagnostics, owing to the expression of specific membrane proteins of their cellular origin. The investigation of epithelial-to-mesenchymal transition (EMT) in cancer using tdEVs is an alternative way of evaluating the risk of malignancy transformation. An ultra-sensitive selection and detection methodology is an essential step in developing a tdEVs-based cancer diagnostic device. In this study, we developed an indium-tin-oxide (ITO) sensor integrated microfluidic device consisting of two main parts: 1) a multi-orifice flow-fractionation (MOFF) channel for extraction of pure EVs by removing blood cellular debris, and 2) an ITO sensor coupled with a geometrically activated surface interaction (GASI) channel for enrichment and quantification of tdEV. The microfluidic channel and the ITO sensors are assembled with a 3D printed magnetic housing to prevent sample leakage and to easily attach/detach the sensors to/from the microfluidic channel. The tdEVs were successfully captured on the specific antibody modified ITO surfaces in the integrated microfluidic channel. The integrated sensors showed an excellent linear response between 103 and 109 tdEVs/mL. Simultaneous evaluation of the epithelial and mesenchymal markers on the tdEV surfaces successfully revealed the EMT index of the corresponding pancreatic cancer cells. Our ITO sensor integrated microfluidic device showed excellent detection in the clinically relevant tdEVs-concentration range for patients with pancreatic cystic neoplasms. Hence, this system is expected to open a new avenue for liquid biopsy-based cancer prognostics and diagnostics.

Improved contact quality for silver-free silicon heterojunction solar cells by phosphoric acid treatment

Electroplating technology is considered as a promising alternative to low-temperature sintered silver pastes for the purpose of significantly reducing the cost of silicon heterojunction (SHJ) solar cells (SCs). However, achieving excellent contact quality between the plated grid and indium tin oxide (ITO) remains a big challenge to satisfy the requirements for fabrication and high performance. In this work, phosphoric acid (H3PO4) is used to modify the ITO surface to improve the contact quality of the plated grid/ITO and enhance the performance of SHJ SCs. It is found that the phosphate groups are adsorbed on the ITO surface to form a dipole layer after H3PO4 treatment. The wettability of H3PO4-treated ITO is substantially improved, resulting in a pinhole-free electroplated nickel (Ni) seed layer. Moreover, the work function of ITO rises by approximately 0.2 eV, which reduces the contact potential barrier between the ITO and the metal electrode. The contact resistivity (ρc) between the plated grid and H3PO4-treated ITO is reduced to approximately 0.4 mΩ·cm2, compared to 1.5 mΩ·cm2 of the control sample. In addition, the metal grid formed on the H3PO4-treated ITO exhibits a better uniformity. Finally, the SHJ cell with H3PO4 treatment process receives a remarkable power conversion efficiency (PCE) of 23.19%, which is approximately 1% (absolute) higher than that of the control device. Therefore, we demonstrate that modifying ITO by H3PO4 is a promising way to improve the contact quality for the electroplating metallization in SHJ SCs.

Formation of nano and micro scale hierarchical structures in MgO and ZnO quantum dots doped LC media: the role of competitive forces

In this paper, we have studied the effect of doping of ZnO and MgO nanoparticles (NPs) in 4-(trans-4-n-hexylcyclo-hexyl) isothiocyanatobenzoate. A thorough comparison of dielectric properties, optoelectronic properties, and calorimetric phase transition properties has been done for MgO and ZnO NP doped LC. We prepare their homogenous mixture of MgO and ZnO NPs in toluene and transfer into cells made of glass and Indium Tin-Oxide (ITO) coated glass. The observed microstructures in the hybrid system can be classified into three main categories: grain like structures formed by aggregation of smaller size MgO nanoparticles while liquid crystal molecules anchor over the surfaces of nanoparticles, the grtu grain-like structures further integrate to form inorganic polymeric type of honeycomb-like mesostructures in presence of glass surface, and flower-like clusters of MgO nanoparticles on ITO surface. The smaller size nanoparticles can maintain the energy balance by allowing the anchoring of liquid crystal molecules over their surfaces whereas the larger size nanoparticles cannot compromise or maintain the energy balance with the liquid crystal molecules and are separated out to nucleate and form bigger size nanoaggregate or clusters. The energy preference of the substrate and nanoparticle’s surface to liquid crystal molecules plays an important role in the formation of different types of hierarchical nano- and microstructures. We account the reasons for the formation of nano and micro scale hierarchical structures on the basis of the competition between the forces: NP-NP, LC-LC, NP-LC, Glass/ITO-NP, and Glass/ITO-LC interactions. We observed a considerable change in the dielectric properties, transition temperature, bandgap, and other parameters of LC molecules when MgO NPs are doped, but a minor change occurs when ZnO NPs are doped in LC. Optical microscopy, FTIR, Raman, IR, HR-XRD and FESEM-EDX characterization data confirm and validate our guiding conceptions.

Enhancement of electronic effects at a biomolecule-inorganic interface by multivalent interactions.

The binding of peptides and proteins through multiple weak interactions is ubiquitous in nature. Biopanning has been used to "hijack" this multivalent binding for the functionalization of surfaces. For practical applications it is important to understand how multivalency influences the binding interactions and the resulting behaviour of the surface. Considering the importance of optimization of the electronic properties of surfaces in diverse electronic and optoelectronic applications, we study here the relation between the multivalency effect and the resulting modulation of the surface work function. We use 12-mer peptides, which were found to strongly bind to oxide surfaces, to functionalize indium tin oxide (ITO) surfaces. We show that the affinity of the peptides for the ITO surface, and concurrently the effect on the ITO work function, are linearly affected by the number of basic residues in the sequence. The multivalent binding interactions lead to a peptide crowding effect, and a stronger modulation of the work function for adodecapeptide than for a single basic amino acid functionalization. The bioderived molecular platform presented herein can pave the way to a novel approach to improve the performance of optoelectronic devices in an eco-friendly manner.

Chronoamperometry-based controllable fabrication of gold nanoparticle monolayers and their hydrophobic force-induced movement on indium tin oxide glass substrate

Owing to their unique plasmonic properties, noble metals have been the materials of choice for photovoltaics, photocatalysis and sensors. Here, we demonstrate novel gold(Au) monolayers with tailorable particle diameters and optical property on transparent indium tin oxide (ITO) using a simple electrochemical deposition. The nanoparticles on ITO are spherical and isolated, and are identified as Au0 nanoparticles. The gold nanoparticles are uniformly distributed on ITO surface, but the gold nanoparticle sizes increase and the particle population densities decrease at lower current densities, resulting in higher light scattering. There is a positive correlation between mean particle size and maximum extinction wavelength of gold nanoparticles prepared with different current densities under a fixed total charge, whereas the maximum extinction wavelength of gold nanoparticles does not change with the total charge under the fixed current densities. The localized surface plasmon resonance change of Au nanoparticles on ITO can be effectively tuned by regulating deposition current density. With the existence of alkanethiols on Au monolayers surface, the original pink color of gold monolayers changed to blue after immersion in toluene for 30 min, indicating hydrophobic force produced by oil-in-water (O/W) or water-in-oil (W/O) phenomenon caused gold nanoparticles to migrate and produce a color change.

An ultra-sensitive electrochemical aptasensor based on Co-MOF/ZIF-8 nano-thin-film by the in-situ electrochemical synthesis for simultaneous detection of multiple biomarkers of breast cancer

This work developed a new electrochemical aptasensor based on the functional hybrid film for simultaneous single step detection of human epidermal growth factor receptor-2 (HER2) and estrogen receptor (ER) biomarkers. The platform is achieved by in-situ electrochemical synthesis of Zn-MOF (ZIF-8) thin film with the conductivity, the specific surface area, and the easy assembly of 2D Co-MOF nanosheets which can adsorbed the amount of aptamer chains on indium tin oxide (ITO) slices. The aptamers were labeled by adsorption of two organic dyes – neutral red (NB) and methylene blue (MB) through electrostatic action, respectively. In the presence of HER2/ER biomarkers, the aptamers of ER/HER2 will combine with ER/HER2 biomarkers to generate new complexes which will far away from the ITO surface due to the specific coupling between MB/NB-labeled single-stranded deoxyribonucleic acid (ssDNA) aptamer and HER2/ER biomarkers is stronger than the aptamer adhered to the Co-MOF/ZIF-8 film on ITO through intermolecular interaction, electrostatic interaction, and π-π stacking. Therefore, it can sensitive single step detection of HER2-ER biomarkers in only 60 min with the detection range are 0 to 15 pg/mL and detection limits as low as 3.8 fg/mL and 6.8 fg/mL, respectively.

Nitrogenous Interlayers for ITO S/D Electrodes in N‐Type Organic Thin Film Transistors

AbstractThe commercialization of organic thin film transistors (OTFTs) is partly hindered by the high cost and stubborn work function (WF) of common Au source/drain (S/D) electrodes. In this work, indium tin oxide (ITO) S/D electrodes modified with three different nitrogenous interlayers including 1,4‐bis(2‐hydroxyethyl) piperazine (HEP), polyethylenimine ethoxylated (PEIE), and branched polyethylenimine (PEI) are adopted to fabricate n‐type OTFTs. The WF of bare ITO is 4.7 eV, whereas ITO modified with nitrogenous interlayers exhibits WFs ranging from 4.1 to 3.6 eV. By the first‐principle calculation and element analysis, the protonated amines are critical for the reduction of ITO surface WF. Besides, the interlayers with higher nitrogen contents are more likely to improve the wettability of octadecyltrichlorosilane (OTS) modified ITO substrates, and help to gain the continuous and oriented poly[2,5‐bis(4‐tetradecyloctadecyl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione‐alt‐5,5′‐di(thiophen‐2‐yl)‐2,2′‐(E)‐1,2‐bis(3,4‐difluorothien‐2‐yl)‐ethene] (P4FTVT‐C32) semiconductor thin films. Therefore, P4FTVT‐C32 based OTFTs with maximum electron field‐effect mobility of 1.95 cm2 V−1 s−1 are achieved by PEI treatments. These results indicate that the ITO S/D electrodes modified by nitrogenous interlayers can greatly slash costs and promote commercialization of OTFTs.

An Evaluation of Surface-Active Agent Hexadecyltrimethylammonium Bromide with Vertical Self-Alignment Properties to Align Liquid Crystals for Various Cell Gap Conditions

We evaluated hexadecyltrimethylammonium bromide (HTAB) for liquid crystals (LCs) in layered ITO cells with various cell gap conditions. HTAB is a surfactant that can self-align vertically on the surface of indium tin oxide (ITO) substrates and induce homeotropic alignment of the LC molecules. For implementing RF devices with HTAB and LCs, we should consider limitations caused by the design conditions which are different from conventional liquid crystal displays such as cell gap. We quantified the concentration of HTAB ([HTAB]) that is necessary to form and maintain a sufficiently dense vertical alignment of 5CB (4-Cyano-4′-pentylbiphenyl). The required [HTAB] for full-homeotropic alignment was increased to the cell gap until it was too large to support the transfer of the surface alignment to the LC molecules, due to the weak anchoring nature of HTAB. We also showed the phase-change characteristic of the LC mixture related to [HTAB] for the design of RF devices driven by light or heat. This study may help to guide the development of new approaches to designing efficient RF devices that use LCs.

An ultrasensitive electrochemical DNA biosensor for monitoring Human papillomavirus-16 (HPV-16) using graphene oxide/Ag/Au nano-biohybrids

A DNA-based electrochemical biosensor has been developed herein for the detection of Human papillomavirus-16 (HPV-16). HPV-16 is a double-stranded, non-enveloped, epitheliotropic DNA virus which responsible for cervical cancer. In this proposed biosensor, an indium tin oxide (ITO) coated glass electrode was modified for sensing HPV-16 using graphene oxide and silver coated gold nanoparticles. Subsequently, HPV-16 specific DNA probes were immobilized on a modified ITO surface. The synthesized nanocomposites were characterized by FE-SEM and UV-VIS spectroscopy techniques. Electrochemical characterization was performed by using cyclic voltammetry and electrochemical Impedance Spectroscopy methods. The hybridization between the probe and target DNA was analyzed by a reduction in current, mediated by methylene blue. The biosensor showed a qualitative inequity between the probe and target HPV-16 DNA. The developed biosensor showed high sensitivity as 0.54 mA/aM for the detection of HPV-16. In a linear range of 100 aM to 1 μM with 100 aM LOD, the proposed biosensor exhibited excellent performance with the rapid diagnosis. Thus, the results indicate that the developed HPV DNA biosensor shows good consistency with the present approaches and opens new opportunities for developing point-of-care devices. The diagnosis of HPV-16 infection in its early stage may also be possible with this detection system.

The enhanced PdAuPt-nitrogen-doped graphene/ITO anode electrodes for electrooxidation of glucose in alkaline medium

The chemical vapor deposition (CVD) method was used to synthesize nitrogen-doped graphene (N-G). N-G coated on Cu foil via CVD method was transferred onto indium tin oxide (ITO). Finally, Pd, Au, and Pt metals were electrochemically doped on the N-G/ITO electrode surface. Surface properties and elemental composition analyses were performed with the obtained electrodes by scanning electron microscope-energy dispersive X-ray (SEM-EDX) and mapping. The results of this analysis indicated that both N-doped G and metals were formed on the ITO surface. The catalytic activity, stability, and resistance of the electrodes for glucose (Glu) electrooxidation were investigated by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) analyses, respectively. The PdAuPt–N-G/ITO electrode exhibited a more active surface area and catalytic activity than the PdAu–N-G/ITO electrode, with a specific activity of 9.50 mA/cm2 and an electrochemical active surface area (ECSA) of 61.21 m2/g. In addition, CA and EIS analyses showed that it was more stable and has faster electron transfer with a lower Rct (143.5 Ω) value. In the light of these results, it can be said that the obtained electrode is promising for glucose electrooxidation.

Influence of Acid-Doped Poly(ethylene imine) Interlayers on the Performance of Polymer:Nonfullerene Solar Cells.

This work reports that ultrathin polymeric films doped with organic acid molecules can act as an electron-transporting interfacial layer in polymer:nonfullerene solar cells. The polymeric interfacial layers, which consist of poly(ethylene imine) (PEI) doped with 3-hydroxypropane-1-sulfonic acid (HPSA) at various HPSA molar ratios, are introduced between transparent indium-tin oxide (ITO) electrodes and polymer:nonfullerene bulk heterojunction layers. The HPSA-doped PEI (PEI:HPSA) films are optically translucent in the wavelength range of ≈300-800nm, while the acidity of PEI solutions reached ≈pH = 7 at HPSA = 30 mol%. The power conversion efficiency of solar cells is improved by doping 20 mol% HPSA due to the increased short circuit current density without open circuit voltage reduction. The improvement in solar cell performances is attributed to an adequate control of HPSA doping ratios, which spares undoped amine units of PEI for making sufficient net dipole layers with ITO surfaces and makes permanent charges for high electrical conductivity in the layers. The surface morphology and doped states are characterized with atomic force microscopy and X-ray photoelectron spectroscopy.

Ultrasensitive and Cost-Effective Detection of Neuropeptide-Y by a Disposable Immunosensor: A New Functionalization Route for Indium-Tin Oxide Surface.

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the human brain, and its levels in the blood change in neurodegenerative and neuroimmune disorders. This indicates that NPY may serve as a diagnostic and monitoring marker for associated disorders. In this paper, an electrochemical immunosensor was created to detect NPY biomarkers using a novel immobilization technique. The proposed biosensor system enables accurate, specific, cost-effective, and practical biomarker analysis. Indium tin oxide-coated polyethylene terephthalate (ITO-PET) sheets were treated with hexamethylene diisocyanate (HMDC) to covalently immobilize antibodies. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques were used to analyze each step of the biosensors. The proposed NPY biosensor has a broad linear detection range (0.01-100 pg mL-1), a low limit of detection (LOD) (0.02968 pg mL-1), and a low limit of quantification (LOQ) (0.0989 pg mL-1). Atomic force microscopy (AFM) was used to support in the optimization process, study the surface morphology, and visualize it. Studies of repeatability, reproducibility, storage, and Kramers-Kronig transformation were conducted during electrochemical characterization. After analytical experiments, the biosensor's responses to human serum samples were evaluated. According to the obtained data, the error margin is small, and the created biosensor offers a great deal of promise for the clinical measurement of NPY.

Nucleation, Coalescence, and Thin-Film Growth of Triflate-Based Ionic Liquids on ITO, Ag, and Au Surfaces

This study investigates the nucleation and growth of micro-/nanodroplets of triflate-based ionic liquids (ILs) fabricated by vapor deposition on different surfaces: indium tin oxide (ITO); silver (Ag); gold (Au). The ILs studied are constituted by the alkylimidazolium cation and the triflate anion—[CnC1im][OTF] series. One of the key issues that determine the potential applications of ILs is the wettability of surfaces. Herein, the wetting behavior was evaluated by changing the cation alkyl chain length (C2 to C10). A reproducible control of the deposition rate was conducted employing Knudsen cells, and the thin-film morphology was evaluated by high-resolution scanning electron microscopy (SEM). The study reported here for the [CnC1im][OTF] series agrees with recent data for the [CnC1im][NTf2] congeners, highlighting the higher wettability of the solid substrates to long-chain alkylimidazolium cations. Compared to [NTf2], the [OTF] series evidenced an even more pronounced wetting ability on Au and coalescence processes of droplets highly intense on ITO. Higher homogeneity and film cohesion were found for cationic groups associated with larger alkyl side chains. An island growth was observed on both Ag and ITO substrates independently of the cation alkyl chain length. The Ag surface promoted the formation of smaller-size droplets. A quantitative analysis of the number of microdroplets formed on Ag and ITO revealed a trend shift around [C6C1im][OTF], emphasizing the effect of the nanostructuration intensification due to the formation of nonpolar continuous domains.

Ionic strength induced local electrodeposition of ZnO nanoparticles

The controlled maskless deposition of nanomaterials locally on surfaces is challenging and of relevance to numerous fields and applications, such as sensing and catalysis. Forming patterns of pre-synthesized, and therefore, well-defined NPs should become a general and simple building approach for manipulating surfaces. Electrochemical deposition of NPs under mild potentials is not common and is based on destabilizing nanomaterial dispersions by an electrical field. This approach that is termed from “nano to nano” is used here for the local deposition of ZnO NPs. Specifically, we employ scanning electrochemical microscopy (SECM) as a means of increasing locally the ionic strength by generating a flux of AuCl4− in a ZnO nanoparticle dispersion. The gold ions bind instantaneously to the ZnO NPs and drive their local deposition on a biased indium tin oxide (ITO) surface to form ZnO nanoparticle patterns embedded in Au. The ratio between Au and ZnO can be changed by controlling the AuCl4− flux at the SECM tip and the ITO potential. The as-electrodeposited ZnO NPs are characterized by microscopy and spectroscopy. Furthermore, the micron-sized Au-ZnO patterns are used as recyclable surface-enhanced Raman scattering (SERS) active substrates for the sensitive detection of a dye. The latter is only an example of the potential of such local nanomaterial-based patterns that can be readily formed by our approach.

Preparation of Spinel Form Co3O4 and CoO2 Thin Film at Low Temperature by Electrochemical Method as a Thin Film Oxide Layer

In this work, thin films of cobalt oxides (CoO2, Co3O4) were prepared using the electrochemical method on the pencil graphite and indium tin oxide surfaces. The substrate effect in the production of both oxides has been studied in detail. While Co3O4 accumulates on the pencil graphite’s surface, CoO2 formation was observed on the indium tin oxide. The characterization of the cobalt oxides was carried out using the X-ray diffraction, Atomic force microscope, and Scanning electron microscope. In this context, the cobalt oxide crystal structure in the range of (−1.0 V)–(+1.9 V) was synthesized on different substrates and at extremely low temperatures (20 °C to 25 °C), using the cyclic voltammetry method, which is a simple one-stage way. Calculated band gap value for ITO/CoO2 as 2.5 eV shows a potential use of this electrode in solar cell applications.

Deciphering the Molecular Mechanism of Substrate-Induced Assembly of Gold Nanocube Arrays toward an Accelerated Electrocatalytic Effect Employing Heterogeneous Diffusion Field Confinement.

The complex electrocatalytic performance of gold nanocubes (AuNCs) is the focus of this work. The faceted shapes of AuNCs and the individual assembly processes at the electrode surfaces define the heterogeneous conditions for the purpose of electrocatalytic processes. Topographic and electron imaging demonstrated slightly rounded AuNC (average of 38 nm) assemblies with sizes of ≤1 μm, where the dominating patterns are (111) and (200) crystallographic planes. The AuNCs significantly impact the electrochemical performance of the investigated electrode [indium–tin oxide (ITO), glassy carbon (GC), and bulk gold] systems driven by surface electrons promoting the catalytic effect. Cyclic voltammetry in combination with scanning electrochemical microscopy allowed us to decipher the molecular mechanism of substrate-induced electrostatic assembly of gold nanocube arrays, revealing that the accelerated electrocatalytic effect should be attributed to the confinement of the heterogeneous diffusion fields with tremendous electrochemically active surface area variations. AuNC drop-casting at ITO, GC, and Au led to various mechanisms of heterogeneous charge transfer; only in the case of GC did the decoration significantly increase the electrochemically active surface area (EASA) and ferrocyanide redox kinetics. For ITO and Au substrates, AuNC drop-casting decreases system dimensionality rather than increasing the EASA, where Au–Au self-diffusion was also observed. Interactions of the gold, ITO, and GC surfaces with themselves and with surfactant CTAB and ferrocyanide molecules were investigated using density functional theory.

Molecularly imprinted conducting polymer based sensor for Salmonella typhimurium detection

This manuscript reports the design and fabrication of conducting plastibody based electrochemical sensor for the detection of Salmonella typhimurium. The conductive plastibody was fabricated on an Indium Tin Oxide surface through potentiostatic method (electrodeposition for 400 s), wherein a polymer mix of pyrrole, lactic acid, ammonium chloride, and sodium dodecyl sulfate was employed for the electrodeposition. Various template removal methods were tested and electrochemical cleaning in the MES buffer was found to be the most suitable, which was optimized further. The synthesized plastibody sensors were characterized using electrochemical impedance spectroscopy, contact angle, FTIR spectroscopy and scanning electron microscopy. Amperometry was used as the electrochemical analytical technique for the determination of the analyte in the concentration range of 100 –108 CFU/mL having a limit of detection of 3.42 CFU/mL. Sensor’s performance was also compared with the non-imprinted electrode and an imprinting factor of 3.8 was found. The plastibody sensor was tested against other bacteria and coefficient of selectivity was calculated to be 1.0, 10.8, 5.6 and 2.4 towards S. typhi, S. aureus, E. coli and L. monocytogenes respectively. The sensor was also found to be reproducible in nature (RSD 0.11 %) and this generic concept presented herein may be extended for the detection of pathogens in other matrices as well.

Editorial Overview: Nanoscale Electrochemistry

A central challenge in electrochemical sciences is that the electrochemical response of an electrode is dominated by nanoscale features on the surface, yet our traditional electrochemical techniques operate on a millimeter or greater length scales. For instance, when we make a cyclic voltammetry measurement on a millimeter-scale electrode, the signal we obtain is based on the average response of all the active sites across the surface while details such as the activities of each site, their spatial distribution, and dynamics cannot be revealed. Nanoscale electrochemistry raises this challenge and has developed a range of techniques to effectively “zoom in” to the micro or nanoscale and, ultimately, to single molecules and atoms, enabling precise measurement of dynamic electrochemical process. This special edition highlights the cutting edge of nanoscale electrochemical research, spanning nanoparticle structure-activity relationships to DNA sequencing and 3D printing. A mainstay of modern nanoscale electrochemistry is the scanning droplet approach known as scanning electrochemical microscopy (SECCM). SECCM simply and effectively restricts an electrochemical measurement to micro or nanoscale region of a large sample surface. In this special edition (Table 1), Schuhmann and co-workers use SECCM to investigate the structure-activity relationships in a high entropy alloy and reveal that active site-specific activities can be detected with probes of dimensions below a micrometer.[1] Takahashi and coworkers use SECCM to investigate the capacitive response of carbon surfaces with 100-nanometer resolution and evaluate the difference in degradation of HOPG occurring at the edge and basal planes.[2] Caleb and co-workers apply a targeted electrochemical cell microscopy (TECCM) approach to isolate the electrocatalytic response of individual shape-controlled nanoparticles toward borohydride oxidation and reveal the significant variations in reactivity and stability for individual nanoparticles.[3] In the review by Bentley, the author summarizes how SECCM has been used to study (nano)particle electrochemistry, often isolated single nanoparticles dispersed on inert supports, and sometimes at sub-particles level.[4] Finally, Momotenko and coworkers review how scanning probe approaches, including but not limited to SECCM, can be utilized for micro and nanoscale electrochemical 3D printing, an innovative strategy for precise fabrication of micro and nanoscale structures.[5] A different approach of electrochemical measurements at nanointerfaces is nano-collision or nano-impact electrochemistry. Shen and Wang demonstrate three different configurations to investigate the size, surface charge, dielectric properties, and electrochemical features of individual graphene oxide sheets.[6] Another approach towards nanoscale electrochemistry is the advanced optical microscopy, where electrochemical processes at nanointerfaces can be imaged with high spatial and temporal resolution by detecting local optical properties. Willets and Bohn investigate the potential-dependent luminescence emission from three different electrofluorogenic probes an indium-tin oxide (ITO) surface.[7] A counterintuitive spectroelectrochemical observation at high irradiance or at low concentration is reported, highlighting the largely ignored importance of interaction between electrofluorogenic probes and ITO surfaces. Finally, we have two opinions that highlight how conductometric electrochemical sensors that make use of nanopores can effectively enable accurate measurements to single molecules. Tan and Ming review how biological nanopores can be used to detect nucleobase modifications in DNA,[8] while Johnson and co-workers elaborate how this approach can be used to sequence double-stranded DNA.[9] To summarize, nanoscale electrochemistry will continue to advance at space and time, revealing the intrinsic features that are often buried and gaining more complete understanding of intricate electrochemical process. Finally, we would like to express our thanks to the Publisher Dr. Brian P. Johnson and Editorial Manager Dr. Jing Tang for their kind supports during the preparation of this special edition. The authors declare no conflict of interest.

(Invited) Immunosensing Chip of Indium Tin Oxide Interdigitated Electrode Array

We introduce three-dimensional (3D) interdigitated electrode array (IDA), which is a pair of IDAs on the ceiling and bottom in a microfluidic channel. The IDAs comprise of Indium tin oxide (ITO) microband electrodes that are alternatively biased. ITO based IDA can be easily and precisely patterned using conventional etching process to be integrated in a single microchannel in which very small volume of liquid sample is enough to fill. Correspondingly requiring extremely small amount of sample, the proposed strategy offers great opportunity for multiplex electrochemical biosensors with high sensitivity. ITO as an electrode material can make 3D IDA more attractive because the limit of detection goes down owing to substantially low background current. Additionally, this serves as a transparent electrode that allows simultaneous optical detection and thus widens the range of options for electrochemical biosensing chip. There are two key issues toward practical analysis. One is reference electrode that needs to lie as closely as possible to working electrodes to minimize iR drop for precise control of electrochemical potential. It is problematic because reference electrode can be hardly miniaturized to be put inside the microchannel with negligible iR drop due to narrow microchannel, i.e. high resistance. The other is functionalization of ITO surface for efficient plan of glass surface as well as ITO microbands. ITO is chemically inert so that few organic molecules can be anchored and any functional layer on it is readily detached to go away. In this presentation, we introduce two-electrode (2E) system that has appropriate mediator layer on ITO IDA. 2E system consists of only two complementary IDA demanding no reference electrodes while electrochemical potential can be retained owing to the mediators lying on the ITO electrodes. And we suggest a more reliable and versatile way of electrografting to firmly pin various mediators onto ITO surface for sensitive electrochemical immunosensing on a chip. Figure 1

Influence of oxygen plasma treatment on structural and spectral changes in gold nanorods immobilized on indium tin oxide surfaces.

Oxygen plasma treatment is commonly used to sterilize gold nanoparticles by removing chemical contaminants from their surface while simultaneously inducing surface activation and functionalization of nanoparticles for biological, electrocatalytic, or electrochemical studies. In this study, we investigate the influence of oxygen plasma treatment on structural and localized surface plasmon resonance (LSPR) spectral changes of anisotropic gold nanorods (AuNRs) immobilized on an indium tin oxide (ITO) glass substrate. Unlike AuNRs deposited on a glass slide, no noticeable structural change or deformation of AuNRs on ITO was observed while increasing the oxygen plasma treatment time. This result indicates that ITO provides structural stability to AuNRs immobilized on its surface. Additionally, single-particle scattering spectra of AuNRs showed the broadening of LSPR linewidth within 60s of oxygen plasma treatment as a result of the plasmon energy loss contributed from plasmon damping to ITO due to the removal of capping material from the AuNR surface. Nevertheless, an increase in the surface charge on the AuNR surface was observed by narrowing the LSPR linewidth after 180s of plasma treatment. The electrochemical study of AuNRs immobilized on ITO electrodes revealed the surface activation and functionalization of AuNRs by increasing plasma treatment. Hence, in this study, a significant understanding of oxygen plasma treatment on AuNRs immobilized on ITO surfaces is provided.