Modified Indium Tin Oxide Surfaces Research Articles

Development of electrode by using gold-platinum alloy nanopar¬ticles for electrochemical detection of serum amyloid A protein

Gold-platinum alloy nanoparticles (AuPtNP) were electrochemically deposited on the surface of indium-tin-oxide (ITO) modified with (3-aminopropyl)triethoxysilane (APTES), after optimizing deposition conditions for the electroplating solution and number of deposition cycles. Different part ratios of Au/Pt used were 4/0, 3/1, 2/2, 1/3 and 0/4 (AuNP, Au3Pt1, Au2Pt2, Au1Pt3 and PtNP, respectively) in preparation of 1 mM solutions. FE-SEM, EDAX and XRD surface characterization techniques were used to confirm the presence of deposited AuPt alloy nanoparticles on the modified ITO surface. Electrochemical methods (CV, DPV and EIS) were used to investigate the electrochemical properties of prepared electrodes in the presence of ferri/ferrocyanide redox couple, which indicated the following increasing order of electrocatalytic peak current: Au < Au2Pt2 < Pt < Au1Pt3 < Au3Pt1. The most active electrode, Au3Pt1NP/APTES/ITO (with Au/Pt part ratio 3:1), was further used to fabricate the immunoelectrode SAA-Ab/Au3Pt1NP/APTES/ITO. The prepared immunoelec­trode was tested for detection of serum amyloid A protein biomarker (APO-SAA) by immobilising SAA-specific antibodies (SAA ½ Ab) on its surface. Sensing studies on this immunoelectrode, performed by DPV technique, revealed the SAA biomarker detection in the linear range of 10 to 106 fg ml-1. The limit of detection was calculated as 7.0 fg ml-1.

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.

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.

Thickness Analyses of 4-(Acetyl Amino)-2-Aminobenzoic Acid on ITO Thin Film Using Analytic Based of X-Ray Photoelectron Spectroscopy Method

In this study, the binding energies of 4-(acetyl amino)-2-aminobenzoic acid molecules that coated on the Indium Tin Oxide (ITO) surface with the self-assembled technique is measured by the XPS method. The thickness of the layer formed on the modified ITO surface is calculated by using XPS technique with an analytical approach. It is reported that the formation of commercially benzoic acid -based self-assembled monolayers (SAMs) is coated surely on ITO that is proved by this technique. According to this approach, the intensity of the substrate-originated photoemission peak from a semi-infinite substrate with a uniform over layer thickness, tXPS(SAM), is obtained from the SAM peak to In3d and Sn3d oxide (ITO) intensity peaks ratio (ISAM/IITO) that the Hill equation allows thin film thickness calculation from XPS data.

Electronic Parameters of Diode Based Organometallic Semiconductor Dyes Centered Ruthenium Complexes with Active COOH Terminals.

In this study, the ruthenium complexes, which is an organometallic N-3 and C-106 semiconductor material, was coated on indium tin oxide (ITO) by using the self-assembled technique and thus a diode containing an organometallic interface was produced. The effects of this interface on the electronic parameters of the diode were investigated. It is aimed to improve the heterogeneity problem of the inorganic/organic interface by chemically bonding these materials from COOH active parts to the ITO surface. In order to understand how the electronic parameters of the diode change with this modification, the Schottky diode electrical characterization approach has been used. The charge mobility of the diode was calculated using the current density-voltage curve (J-V) characteristic with Space Charge Limited Current (SCLC) technique. When the electrical field is applied to the diode, it can be said that the ruthenium complexes molecules create an electrical dipole and the tunneling current is transferred to the anode contact ITO through the ruthenium molecule through the charge carrier, thus contributing to the hole injection. The morphology of these interface modifications was examined by Atomic Force Microscope (AFM) and surface potential energy by KelvinProbe Force Microscope (KPFM). To investigate local conductivity of bare ITO and modified ITO surface, Scanning Spreading Resistance Microscopy (SSRM) that is a conductive AFM analyzing technique were performed by applying voltage to the conductive tip and to the sample. According to the results of this work the diode containing N-3 material shows the best performance in terms of charge injection to the ITO due to possess the lowest barrier height Φb as 0.43 eV.

IMPROVEMENT OF SURFACE POTENTIAL ENERGY OF INDIUM TIN OXIDE THIN FILM MODIFIED WITH ORGANIC SEMICONDUCTOR MATERIAL BASED ON PHENYL GROUP

This study focuses on surface characterization of modified indium tin oxide (ITO) for potential applications as anode in organic electronics devices. [4-iodophenyl]-silanetriol molecules were coated by self-assembled monolayers method on ITO surface. Kelvin Probe Microscopy, Scanning Tunneling Microcopy and X-ray Photoelectron Spectroscopy techniques were used to analyze the modified ITO surface. The results show that organic semiconductor material based on Phenyl group enhance surface morphology and increase the surface potential energy of ITO around [Formula: see text][Formula: see text]meV and contribute the tunneling current that inject from Fermi energy level of the ITO. This study includes the influence of surface interactions on electrochemical and spectral features of compounds. The results are important in developing surface structures in amorphous layers, better understanding the mechanism of creation of such structures on ITO surface.

Zinc Phthalocyanine–Phosphonic Acid Monolayers on ITO: Influence of Molecular Orientation, Aggregation, and Tunneling Distance on Charge-Transfer Kinetics

Efficient charge harvesting at electrodes is critical for the effective performance of organic photovoltaics and is strongly influenced by the first molecular monolayer at the transparent conducting oxide electrode. Herein, we present a study of the relationship between molecular orientation and tunneling distance on charge-transfer rates between a tethered sub-monolayer/monolayer of phosphonic acid (PA)-functionalized Zn phthalocyanines (ZnPcs) and an indium tin oxide (ITO) surface by a combination of electrochemical techniques and waveguide tools such as attenuated total reflectance (ATR) UV–vis spectroscopy and potential-modulated ATR (PM-ATR) spectroelectrochemistry. The distance between the main chromophore and PA anchoring group was modulated by an aliphatic carbon of various lengths (n = 3, 9, 10, or 11) that resulted in an extended distance of 7–18 Å between the ZnPcs and the ITO surface. Modified ITO surfaces were composed of monomeric and aggregated subpopulations of ZnPcs with molecular orientations predominantly in-plane (36–39°) and out-of-plane (72–75°), respectively. Charge-transfer rate constants (ks,opt) were measured using PM-ATR. For a given tether length, the aggregated subpopulations exhibit higher ks,opt values compared to the monomeric subpopulations. The observed ks,opt values had an exponential dependence on the effective tunneling distance with a decay constant (β) that ranged from 0.32 to 0.47 Å–1, depending on the chromophore orientation and aggregation state. The fastest charge-transfer rate constants were found for the chromophores with the smallest tunneling distance (n = 3). A ks,opt of 3.9 × 104 s–1 represents the fastest rate constant measured by PM-ATR for a PA-functionalized ZnPc chromophore tethered to an ITO waveguide electrode.

Interfacial Electron Transfer of Ferrocene Immobilized onto Indium Tin Oxide through Covalent and Noncovalent Interactions.

The immobilization of molecular species onto electrodes presents a direct route to modifying surface properties with molecular fidelity. Conventional methods include direct covalent attachment and physisorption of pyrene-appended molecular compounds to electrodes with aromatic character through π-π interactions. A recently reported hybrid approach extends the synthetic flexibility of the latter to a broader range of electrode materials. We report an application of this approach to immobilization of pyrene-appended ferrocene onto pyrene-functionalized indium tin oxide (ITO). The modified ITO surfaces were characterized using X-ray photoelectron spectroscopy, fluorescence spectroscopy, and electrochemical techniques. An electron-transfer rate constant ( kapp) of 100 ± 8 s-1 was measured between the electrode and immobilized ferrocene using electrochemical methods. For comparison, a ferrocene-modified electrode using conventional covalent attachment of vinylferrocene was also prepared, and kapp was measured to be 9 ± 2 s-1.

Poly-L-lysine modified ITO surface for enhanced cell growth

Material surface properties are considered as critical factor for the study of in Vitro cell growth and activities. It provides advantages not only for study of cellular activity but also for biomedical technology such as tissue engineering. Neuron is a typical cell type widely used to examine cell communications, alignments and differentiations. In the present study, a simple pattern of indium tin oxide (ITO) for neuron culture is introduced. Circular inter-digitated design of ITO platform was fabricated by using simple photolithography techniques. In order to enhance cell attachment, the fabricated electrode surface was modified by poly-L-lysine, a positive charge molecule that allows binding site for cell adhesion. SH-SY5Y cell, a human neuroblastoma cell line, was cultured on the modified surface. Results show that cells preferably adhere on the ITO surface while some of them align itself according to the ITO pattern. In addition, the possibility of fabricated nanostructure platform can indicate the potential control of cell precisely guidance and pattern on surface.

Phosphonic Acid Functionalized Asymmetric Phthalocyanines: Synthesis, Modification of Indium Tin Oxide, and Charge Transfer

Metalated and free-base A(3)B-type asymmetric phthalocyanines (Pcs) bearing, in the asymmetric quadrant, a flexible alkyl linker of varying chain lengths terminating in a phosphonic acid (PA) group have been synthesized. Two parallel series of asymmetric Pc derivatives bearing aryloxy and arylthio substituents are reported, and their synthesis and characterization through NMR, combustion analysis, and MALDI-MS are described. We also demonstrate the modification of indium tin oxide (ITO) substrates using the PA functionalized asymmetric Pc derivatives and monitoring their electrochemistry. The PA functionalized asymmetric Pcs were anchored to the ITO surface through chemisorption and their electrochemical properties characterized using cyclic voltammetry to investigate the effects of PA structure on the thermodynamics and kinetics of charge transfer. Ionization energies of the modified ITO surfaces were measured using ultraviolet photoemission spectroscopy.

Importance of the Indium Tin Oxide Substrate on the Quality of Self-Assembled Monolayers Formed from Organophosphonic Acids

The role of indium tin oxide (ITO) surface structure and chemistry on the formation of self-assembled monolayers (SAM) derived from organophosphonic acids has been investigated. The surface hydroxide content, crystal structure, and roughness of unmodified ITO surfaces were analyzed with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and contact angle measurements. Organophosphonic acid monolayer modified ITO surfaces were then characterized using electrochemistry, contact angle measurements and impedance spectroscopy. To ascertain the extent of defects, Pb was underpotentially deposited (UPD) onto the monolayer modified ITO surfaces at defect sites and regions where the monolayer was weakly bound. The extent of defects, and the location of defects, in monolayers formed on different ITO surfaces were determined from the amount of charge passed during UPD of Pb at identical conditions, followed by XPS analysis of the Pb 4f peak and imaging with scanning tunnelling microscopy (STM). The results demonstrate that the crystal structure and hydroxide ion concentration of ITO surfaces significantly influence the quality of self-assembled monolayer formation as does the surface roughness. The most well-packed stable monolayers formed only on smooth amorphous ITO substrates with homogeneous grains and high hydroxide content. Lower quality SAMs with significant defects formed on polycrystalline surfaces and the higher the roughness the more the defects. STM defect mapping revealed that the location of defects in monolayers occurred at the boundaries between grain edges on the polycrystalline surfaces. This shows that the substrate characteristics have a strong influence on the quality of monolayers formed on ITO surfaces.

Direct Growth of Gold Nanorods on Gold and Indium Tin Oxide Surfaces: Spectral, Electrochemical, and Electrocatalytic Studies

The surfactant-assisted seed-mediated growth method was used for the formation of gold nanorods (GNRs) directly on gold (Au) and indium tin oxide (ITO) surfaces. Citrate-stabilized ∼2.6 nm spherical gold nanoparticles (AuNPs) were first self-assembled on ITO or Au surfaces modified with (3-mercaptopropyl)-trimethoxysilane (MPTS) sol−gel film and then immersed in a cationic surfactant growth solution to form GNRs. The growth of GNRs on the MPTS sol−gel film modified ITO surface was monitored by UV−visible spectroscopy. The ITO surface with the attached spherical AuNPs shows a surface plasmon resonance band at 550 nm. The intensity of this absorption band increases while increasing the immersion time of the AuNP-modified ITO surface into the growth solution, and after 5 h, an additional shoulder band around 680 nm was observed. The intensity of this shoulder band increases, and it was shifted to longer wavelength as the immersion time of the AuNP-modified ITO surface into the growth solution increases. After 20 h, a predominant wave at 720 nm was observed along with a band at 550 nm. Further immersion of the modified ITO surface into the growth solution did not change the absorption characteristics. The bands observed at 550 and 720 nm were characteristics of GNRs, corresponding to transverse and longitudinal waves, respectively. The AFM images showed the presence of GNRs on the surface of the MPTS sol−gel modified ITO surface with a typical length of ∼100−120 nm and a width of ∼20−22 nm in addition to a few spherical AuNPs, indicating that seeded spherical AuNPs were not completely involved in the GNRs’ formation. Finally, the electrocatalytic activity of the surface-grown GNRs on the MPTS sol−gel film modified Au electrode toward the oxidation of ascorbic acid (AA) was studied. Unlike a polycrystalline Au electrode, the surface-grown GNR-modified electrode shows two well-defined voltammetric peaks for AA at 0.01 and 0.35 V in alkaline, neutral, and acidic pHs. The cause for the observed two oxidation peaks for AA was due to the presence of both nanorods and spherical nanoparticles on the electrode surface. The presence of spherical AuNPs on the MPTS sol−gel film oxidized AA at more positive potential, whereas the GNRs oxidized AA at less positive potential. The observed 340 mV less positive potential shift in the oxidation of AA suggested that GNRs are better electrocatalysts for the oxidation of AA than the spherical AuNPs.

Ferrocene Functional Polymer Brushes on Indium Tin Oxide via Surface-Initiated Atom Transfer Radical Polymerization

The synthesis and electrochemical characterization of ferrocene functional polymethacrylate brushes on indium tin oxide (ITO) electrodes using surface-initiated atom transfer radical polymerization (SI-ATRP) is reported. SI-ATRP of ferrocene-containing methacrylate (FcMA) monomers from a phosphonic acid initiator-modified ITO substrate yielded well-defined homo- and block (co)polymer brushes of varying molar mass (4,000 to 37,000 g/mol). Correlation of both electrochemical properties and brush thicknesses confirmed controlled SI-ATRP from modified ITO surfaces. The preparation of block copolymer brushes with varying sequences of FcMA segments was conducted to interrogate the effects of spacing from the ITO electrode surface on the electrochemical properties of a tethered electroactive film.

Selective deposition of semiconducting single-walled carbon nanotubes onto amino-silane modified indium tin-oxide surface for the development of poly(3-hexylthiophene)/carbon-nanotube photovoltaic heterojunctions

A method is described to obtain separation of single-walled carbon nanotubes (SWCNTs) on an indium tin-oxide (ITO) substrate by modifying the conducting surface of ITO with amino-silane functional groups. Scanning electron microscopy confirmed that the amino-silane functionalization of the substrate is a critical parameter for the immobilization of separated nanotubes. In particular spin coating the SWCNT solution onto the amino-silane modified ITO surface results in a lower nanotube density with respect to the reference sample obtained on pure ITO together with the immobilization of semiconducting carbon nanotubes onto the substrate. The possibility of using these SWCNT thin films to obtain polymer/nanotube heterojunctions for the development of organic solar cells is considered.

Immobilization of albumin on indium-tin oxide (ITO) surface via isocyanate linkage

Indium-tin oxide (ITO) surfaces have become a very important material for use as a conducting substrate, recently. Immobilization of biological molecule onto the ITO is a fundamental step in the development of biosensors. In this paper, attachment of albumin was carried out using ITO as a support. Albumin was covalently immobilized onto self–assembled monolayer (SAM) of (3-isocyanatopropyl) triethoxysilane (IPTES) on ITO surface. Isocyanato-functionalized organic film was prepared by self–assembling on active ITO surface. After that, human serum albumin (HAS) which was prepared in Phosphate-Buffered Saline Solution (PBS: pH 7.4, 0.1 M), was covalently immobilized on IPTES modified ITO surface. The study here can help us understand the influence of monolayer and electrochemical behavior on ITO surface. Characterization of stepwise changes of active ITO, IPTES/ITO and albumin/IPTES/ITO surfaces were carried out using contact angle (CA) measurements, fluorescence microscopy, atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), respectively.

Self‐assembled Electroactive Phosphonic Acids on ITO: Maximizing Hole‐Injection in Polymer Light‐Emitting Diodes

AbstractIn order to fulfill the promise of organic electronic devices, performance‐limiting factors, such as the energetic discontinuity of the material interfaces, must be overcome. Here, improved performance of polymer light‐emitting diodes (PLEDs) is demonstrated using self‐assembled monolayers (SAMs) of triarylamine‐based hole‐transporting molecules with phosphonic acid‐binding groups to modify the surface of the indium tin oxide (ITO) anode. The modified ITO surfaces are used in multilayer PLEDs, in which a green‐emitting polymer, poly[2,7‐(9,9‐dihexylfluorene)‐co‐4,7‐(2,1,3‐benzothiadiazole)] (PFBT5), is sandwiched between a thermally crosslinked hole‐transporting layer (HTL) and an electron‐transporting layer (ETL). All tetraphenyl‐diamine (TPD)‐based SAMs show significantly improved hole‐injection between ITO and the HTL compared to oxygen plasma‐treated ITO and simple aromatic SAMs on ITO. The device performance is consistent with the hole‐transporting properties of triarylamine groups (measured by electrochemical measurements) and improved surface energy matching with the HTL. The turn‐on voltage of the devices using SAM‐modified anodes can be lowered by up to 3 V compared to bare ITO, yielding up to 18‐fold increases in current density and up to 17‐fold increases in brightness at 10 V. Variations in hole‐injection and turn‐on voltage between the different TPD‐based molecules are attributed to the position of alkyl‐spacers within the molecules.

Contact resistance between pentacene and indium–tin oxide (ITO) electrode with surface treatment

Contact resistance between indium–tin oxide (ITO) electrode and pentacene was studied by transmission line method (TLM). Organic solvent cleaned, inorganic alkali cleaned, and self-assembled monolayer (with OTS: octadecyltrichlorosilane) modified ITO electrode structures were compared. Pentacene layer of 300 Å thickness was vacuum deposited on patterned ITO layer at 70 °C with a deposition rate of 0.3 Å/s. Alkali cleaned and SAM modified ITO gave a lower contact resistance of about 6.34 × 10 4 Ω cm 2 and 1.88 × 10 3 Ω cm 2, respectively than organic solvent cleaned ITO of about 6.58 × 10 5 Ω cm 2. Especially with the SAM treatment, the work function of ITO increased closer to the highest occupied molecular orbital (HOMO) level of pentacene, which lowers the injection barrier between ITO and pentacene. It was also believed that pentacene morphology was improved on SAM modified ITO surface due to the lowering of the surface energy. We could obtain the low contact resistance with SAM treatment which is comparable to the measured value of gold–pentacene contact, 1.86 × 10 3 Ω cm 2. This specific contact resistance is still much higher than that of amorphous silicon thin film transistor (0.1–30 Ω cm 2).

Transparent low-work-function indium tin oxide electrode obtainedby molecular scale interface engineering

A redox reaction between a monolayer of electron–donor molecules, tetrakis(dimethylamino)ethylene, and the indium tin oxide (ITO) surface results in a decrease of the ITO work function down to 3.7eV. The modified ITO surface may be used as electron injecting electrode in polymer light-emitting devices. Photoelectron spectroscopy measurements show that the low-work-function of the modified electrode remains upon exposure to air or gentle annealing; thus, making it a good candidate for inexpensive fabrication of organic/polymeric (opto)electronic devices.