ITO Electrode Surface Research Articles

Synthetic Mn3Ce2O5-Cluster Mimicking the Oxygen-Evolving Center in Photosynthesis.

The photosynthetic oxygen-evolving center (OEC) is a unique Mn4CaO5-cluster that catalyses water splitting into electrons, protons, and dioxygen. Precisely structural and functional mimicking of the OEC is a long-standing challenge and pressingly needed for understanding the structure-function relationship and catalytic mechanism of O-O bond formation. Herein we report two simple and robust artificial Mn3Ce2O5-complexes that display a remarkable structural similarity to the OEC in regarding of the ten-atom core (five metal ions and five oxygen bridges) and the alkyl carboxylate peripheral ligands. This Mn3Ce2O5-cluster can catalyse the water-splitting reaction on the surface of ITO electrode. These results clearly show that cerium can structurally and functionally replace both calcium and manganese in the cluster. Mass spectroscopic measurements demonstrate that the oxide bridges in the cluster are exchangeable and can be rapidly replaced by the isotopic oxygen of H2 18O in acetonitrile solution, which supports that the oxide bridge(s) may serve as the active site for the formation of O-O bond during the water-splitting reaction. These results would contribute to our understanding of the structure-reactivity relationship of both natural and artificial clusters and shed new light on the development of efficient water-splitting catalysts in artificial photosynthesis.

Highly Efficient Photoelectrochemical Detection of Cystatin C Based on a Core-Shell MOF Nanocomposite with Biomimetic-Catalysis Amplification.

Cystatin C (CysC) has been proven to be used to diagnose acute kidney injury (AKI) rapidly and sensitively early. Therefore, it is urgent to develop a sensitive, novel, and rapid method for detecting CysC. In this work, a novel photoelectrochemical (PEC) biosensor was designed for ultrasensitive CysC detection. Ti-MOF@DM-LZU1@Au as a photosensitive material was first modified on the ITO electrode surface. Then, Ab1 and CysC were assembled on the electrode via the specific immunoresponse of an antigen and antibody. Lastly, the conjugate Ab2/l-Cys bilayer/l-Cys-hemin/G-quadruplex with self-catalytic enzyme performance, as a signal amplification approach, could further react with CysC and Ab1, which resulted in a stronger photocurrent. As expected, the constructed PEC sensor realized the ultrasensitive detection of CysC, with a detection range of 10 pg/mL to 16 μg/mL and a lower limit of 8.023 pg/mL. The biosensor had excellent repeatability, selectivity, and stability. Moreover, it can provide a new method for the sensitive and rapid detection of other protein molecules in clinical practice.

Molecularly imprinted orthophenylenediamine with Ti3C2TxMXene‐based biosensor for sensitive detection of bilirubin

AbstractIn this study, bilirubin (BR) is detected by using a novel molecularly imprinted electrochemical sensor based on a Ti3C2TxMXene‐modified ITO electrode. First, Ti3C2TxMXene is synthesized by chemical etching and deposited at the ITO electrode surface by drop casting. After that, ortho‐phenylenediamine (o‐PD) as monomer is electropolymerized in the presence of a sodium acetate buffer solution containing the BR template to prepare BR‐imprinted electrode. Field emission scanning electron microscopy (FESEM), x‐ray diffraction and UV–visible absorption spectroscopy confirms the MXene synthesis. The molecular imprinted polymer (MIP) formation at the electrode is confirmed by electrochemical methods such as differential pulse voltammetry, electrochemical impedance spectroscopy, and cyclic voltammetry, and FESEM. The linearity range, limit of detection and the limit of quantification are calculated as 0.1 mg/dL to 20 mg/dL, 0.002 mg/dL, and 6.6 mg/dL respectively. Stability and reproducibility are also reported for the prepared MIP sensor.

Electrochemiluminescent imaging of a NADH-based enzymatic reaction confined within giant liposomes.

Herein, transient releases either from NADH-loaded liposomes or enzymatic reactions confined in giant liposomes were imaged by electrochemiluminescence (ECL). NADH was first encapsulated with the [Ru(bpy)3]2+ luminophore inside giant liposomes (around 100µm in diameter) made of DOPC/DOPG phospholipids (i.e., 1,2-dioleolyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycerol-3-phospho-(1'-rac-glycerol) sodium salt) on their inner- and outer-leaflet, respectively. Then, membrane permeabilization triggered upon contact between the liposome and a polarized ITO electrode surface and ECL was locally generated. Combination of amperometry, photoluminescence, and ECL provided a comprehensive monitoring of a single liposome opening and content release. In a second part, the work is focused on the ECL characterization of NADH produced by glucose dehydrogenase (GDH)-catalyzed oxidation of glucose in the confined environment delimited by the liposome membrane. This was achieved by encapsulating both the ECL and catalytic reagents (i.e., the GDH, glucose, NAD+, and [Ru(bpy)3]2+) in the liposome. In accordance with the results obtained, NADH can be used as a biologically compatible ECL co-reactant to image membrane permeabilization events of giant liposomes. Under these conditions, the ECL signal duration was rather long (around 10s). Since many enzymatic reactions involve the NADH/NAD+ redox couple, this work opens up interesting prospects for the characterization of enzymatic reactions taking place notably in artificial cells and in confined environments.

Electrically triggered photonic crystal anti-counterfeiting tags with multi-level response fabricated by regioselective modification of ITO electrode surface

Anticounterfeiting materials based on the photonic crystal (PC) have attracted great interest due to their unique visual effects originating from the changeable structural colors under various external stimuli. However, there still are challenges to improving the anticounterfeiting performance by enhancing the complexity and diversity of the color changes. Here, we fabricated an electrically triggered anticounterfeiting tag by encapsulating the responsive PC with the surface-modified and patterned ITO electrode. The degree of Au deposition or chemical etching in different regions of the ITO was precisely controlled to achieve multi-level differentiated electrical responses, which made the invisible pattern of the tag at 0 V be “revealed in multicolor form” or “gradually revealed” under increasing voltages. The tag possessed two working modes, more diversified visual effects, good usability, and reversibility, which let it become a potentially useful material for anti-counterfeiting applications in the future.

Shadow electrochemiluminescence imaging of giant liposomes opening at polarized electrodes.

In this work, the release of giant liposome (∼100 μm in diameter) content was imaged by shadow electrochemiluminescence (ECL) microscopy. Giant unilamellar liposomes were pre-loaded with a sucrose solution and allowed to sediment at an ITO electrode surface immersed in a solution containing a luminophore ([Ru(bpy)3]2+) and a sacrificial co-reactant (tri-n-propylamine). Upon polarization, the electrode exhibited illumination over its entire surface thanks to the oxidation of ECL reagents. However, as soon as liposomes reached the electrode surface, dark spots appeared and then spread over time on the surface. This observation reflected a blockage of the electrode surface at the contact point between the liposome and the electrode surface, followed by the dilution of ECL reagents after the rupture of the liposome membrane and release of its internal ECL-inactive solution. Interestingly, ECL reappeared in areas where it initially faded, indicating back-diffusion of ECL reagents towards the previously diluted area and thus confirming liposome permeabilization. The whole process was analyzed qualitatively and quantitatively within the defined region of interest. Two mass transport regimes were identified: a gravity-driven spreading process when the liposome releases its content leading to ECL vanishing and a diffusive regime when ECL recovers. The reported shadow ECL microscopy should find promising applications for the imaging of transient events such as molecular species released by artificial or biological vesicles.

Co-reactant confined and vertically ordered silica nanochannel regulated electrochemiluminescence for homogeneous detection of miRNA

Electrochemiluminescence (ECL) arises from the collisional annihilation between the electro-excited luminophore and co-reactant. Most ECL-based bioassays require extensive free co-reactants that collide with luminophores randomly. Herein, the N,N-dimethylaniline (DMA) group was electro-grafted on the ITO electrode surface as the bottom co-reactant layer, and the vertically ordered mesoporous silica film (VMSF) was prepared as the upper layer to regulate the accessibility of Ru(bpy)32+. Thus, the dual-layer functionalized VMSF/N-ITO was newly built for the controllable ECL study. Relevant conditions, including the DMA electro-grafting, VMSF thickness, buffer concentration and pH value, were discussed to improve the ECL efficiency. Based on the VMSF/N-ITO platform, a homogeneous ECL bioassay was developed for miRNA-21 detection. The target nucleotide sequence induced the hybridization chain reaction (HCR) of probes H1 and H2 to absorb free Ru(bpy)32+ as much as possible. Residual Ru(bpy)32+ permeated the VMSF nanochannels to collide with the DMA co-reactant in producing an ECL response. There was a linear relationship between ∆ECL intensity and logarithmic concentration of miRNA-21 in the 1 fM ∼ 100 pM range, and the detection limit was 0.25 fM. The developed approach was probes immobilization-free, highly sensitive, and anti-interference, opening a new avenue for ECL-based bioassays.

A near-infrared photoelectrochemical aptasensing system based on Bi2O2S nanoflowers and gold nanoparticles for high-performance determination of MCF-7 cells

Circulating tumor cells (CTCs) are commonly considered as the major cause of tumor metastasis and can eventually lead to death. Therefore, developing a high-performance method for the determination of CTCs is very significant for promoting the cancer survival rate. Photoelectrochemical biosensing systems have been extensively investigated and applied for bioassays. Herein, Bi2O2S nanoflowers were successfully prepared through a simple one-step hydrothermal method. After being integrated with gold nanoparticles with a diameter of ∼45 nm, AuNPs/Bi2O2S nanocomposites were coated onto an ITO electrode surface to build a photoelectrochemical sensing platform which can be excited with near-infrared light to produce photocurrent response. Subsequently, mercapto-group functionalized aptamer (SH-Apt) was fixed onto the AuNPs/Bi2O2S/ITO surface. Due to the overexpress of MUC1 protein in the cell membrane, MCF-7 cells were specifically trapped on the SH-Apt/AuNPs/Bi2O2S/ITO surface. The introduce of MCF-7 cells lead to an obvious decrease on the photocurrent response. The photocurrent variation shows a satisfied linear relationship to the logarithm of MCF-7 cells concentration ranged from 50 to 6 × 105 cell mL−1. The detection limit obtained is 17 cell mL−1. The PEC biosensor shows excellent sensitivity, selectivity and stability for sensing MCF-7 cells, even for determining MCF-7 cells in clinical serum samples.

Preparation, optical and electrochemical properties of unsymmetrical tetrazaporphyrins with a diarylchalcogenophene unit

Unsymmetrically substituted tetraazaporphyrins, dithienylthienotris(dialkyloxybenzo)tetraazaporphyrins (alkyl = butyl and octyl), were prepared by the reaction of 2,5-dithienyl-3,4-dicyanothiophene with 2,5-di(alkyloxy)phthalonitriles in the presence of lithium alkoxide. Similar reactions of 3,4-dicyanothiophene, 2,5-diphenyl-3,4-dicyanothiophene, and 2,5-diphenyl-3,4-dicyanoselenophene with 2,5-di(octyloxy)phthalonitrile gave thieno, diphenylthieno, and diphenylselenolotris(dioctyloxybenzo)tetraazaporphyrins, respectively. The structures of the products were determined by 1H NMR spectroscopy and high-resolution FAB MS spectrometry. Optical and electrochemical properties of the products were determined by UV–vis spectroscopy and cyclic voltammetry using Ag/AgNO3 as a reference electrode (solvent: dichloromethane; counter electrode: Pt; electrolyte: n-Bu4NClO4). An insoluble thin film was produced on the glassy carbon and ITO electrode surfaces by the electrochemical oxidation of dithienylthienotris(dibutoxybenzo)tetraazaporphyrin. The optical and electrochemical properties of the film were determined by UV–vis spectroscopy and cyclic voltammetry. The structures of simplified model compounds were optimized using the DFT method with the Gaussian 09 program at the B3LYP/6-31G(d,p) level.

A photoelectrochemical sensor combining CS−GSH−CuNCs and xanthine oxidase for the detection of xanthine

AbstractA photoelectrochemical (PEC) sensor combining chitosan‐coated and glutathione‐protected copper nanocluster (CS−GSH−CuNCs) with peroxidase‐like activity and xanthine oxidase (XAO) was developed for rapid detection of xanthine. Firstly, CS−GSH−CuNCs was prepared by glutathione (GSH) reduction using chitosan (CS) as protective agent, and then was modified on titanium dioxide nanoparticles (TiO2 NPs)/ITO electrode which was prepared by sintering titanium dioxide (TiO2) on the ITO electrode surface by high temperature calcination. After excited by light at 350 nm, the photoinduced electrons from the lowest unoccupied molecular orbital (LUMO) of CS−GSH−CuNCs were transferred to the conduction band of TiO2, which resulted in spatial separation of electron‐hole and enhancement of photocurrent signal. XAO oxidizes xanthine to produce hydrogen peroxide (H2O2). Part of the photoinduced electrons from CS−GSH−CuNCs transferred and catalyzed the reduction of H2O2, resulting in the reduction of the photocurrent. Under optimal conditions, the PEC sensor exhibits good sensitivity and reproducibility with the limit of detection (LOD) of 6.6 nmol ⋅ L−1 and a relative standard deviation of 3.5 % for 10 replicate detections of 1.00 μmol ⋅ L−1 xanthine and the linear range of 0.04–90.0 μmol ⋅ L−1 for xanthine. Furthermore, the PEC sensor presents nice selectivity owing to its enzyme‐like activity and was successfully applied to human urine, indicating its great potential for real sample analysis.

Sensitive photoelectrochemical detection of colitoxin DNA based on NCDs@CuO/ZnO heterostructured nanocomposites with efficient separation capacity of photo-induced carriers.

Ametal-organic framework (MOF) of Cu-TPA (terephthalic acid) microsphere was prepared, followed by calcinating the MOF precursor of Cu-TPA/ZIF-8 mixture to obtain the CuO/ZnO. N-doped carbon dots (NCDs) were employed to combine the CuO/ZnO composite to form a tripartite heterostructured architecture of NCDs@CuO/ZnO, which led to a fierce enlargement of the photocurrent response. This was ascribed to the thinner-shell structure of the CuO microsphere and the fact thathollow ZnO particles could sharply promote the incidence intensity of visible light. The more porous defectiveness exposed on CuO/ZnO surface was in favor of rapidly infiltrating electrolyte ions. The p-n type CuO/ZnO composite with more contact interface could abridge the transfer distance of photo-induced electron (e-1)/hole (h+) pairs and repress their recombination availably. NCDs not only could boost electron transfer rate on the electrode interface but also successfully sensitized the CuO/ZnO composite, which resulted in high conversion efficiency of photon-to-electron. The probe DNA (S1) was firmly assembled on the modified ITO electrode surface (S1/NCDs@CuO/ZnO) through an amidation reaction. Under optimal conditions, the prepared DNA biosensor displayed a wide linear range of 1.0 × 10-6 ~ 7.5 × 10-1nM and a low limit of detection (LOD) of 1.81 × 10-7nM for colitoxin DNA (S2) measure, which exhibited a better photoelectrochemistry (PEC) analysis performance than that obtained by differential pulse voltammetry techniques. The relative standard deviation (RSD) of the sensing platform for target DNA detection of 5.0 × 10-2nM was 6.3%. This proposed DNA biosensor also showed good selectivity, stability, and reproducibility, demonstrating that the well-designed and synthesized photoactive materials of NCDs@CuO/ZnO are promising candidates forPEC analysis.

Study on Catalytic Water Oxidation Properties of Polynuclear Manganese Containing Polyoxometalates

Splitting of water to produce hydrogen and oxygen is a green and effective method to produce clean energy. Finding an efficient water decomposition catalyst is the key step to realize water decomposition. In this work, by choosing from the literature, six polynuclear manganese (Mn) containing polyoxometalates (Mn-POMs) with different Mn-O clusters and oxidation states of Mn, [MnIIMnIIISiW10O37(OH)(H2O)]6− (Mn2-POM), [MnII3MnIII(H2O)2(PW9O34)2]9− (Mn4-POM), [MnII4MnIII2Ge3W24O94(H2O)2]18− (Mn6-POM-1), [MnIII2MnII4(μ3-O)2(H2O)4(B-β-SiW8O31)(B-β-SiW9O34)(γ-SiW10O36)]18− (Mn6-POM-4), [{MnIII3MnIV4O4(OH)2(OH2)}2(W6O22)(H2W8O32)2(H4W13O46)2]26− (Mn14-POM), [MnII19 (OH)12(SiW10O37)6]34− (Mn19-POM) were prepared. First, the catalytic performance towards the water oxidation of six Mn-POMs was investigated in solution for the first time. Second, six Mn-POMs were fabricated on the surface of ITO electrode using layer-by-layer self-assembly (LBL) to form the composite films, which were characterized by UV-vis spectroscopy and cyclic voltammetry, and then the catalytic water oxidation performance of the composite films was studied and compared with that in solution via a series of controlled experiments, the results indicate that the Mn-POMs with three-dimensional structures, which contain variable valence Mn-O cluster similar to the structure of photocatalytic active center (PSII) exhibit better catalytic performance.

Ultrasensitive Homogeneous Electrochemiluminescence Biosensor for a Transcription Factor Based on Target-Modulated Proximity Hybridization and Exonuclease III-Powered Recycling Amplification.

Herein an ultrasensitive homogeneous ECL biosensor has been developed for TF NF-κB p50 through target-modulated proximity hybridization coupling with exonuclease III (Exo III)-powered recycling amplification. The ECL reagent (Ru(bpy)32+)-labeled hairpin DNA (HP-Rul) contains many negatively charged phosphates on the DNA chain, which cannot diffuse easily toward the negatively charged ITO electrode surface because of the large electrostatic repulsion. So a weak ECL signal can be detected. A proximity complex containing partial double strand DNA (dsDNA, as the binding site) and two hanging single-stranded DNA (ssDNA) fragments has been designed. The binding of NF-κB p50 to dsDNA effectively protects the proximity complex from digestion, forming a stable TF-DNA complex. ssDNA hybridizes with HP-Rul through proximity hybridization and hence forms a T-shape structure. This structure can be recognized by Exo III, thereby initiating the digestion process and results in the release of Ru(bpy)32+-labeled mononucleotide fragments (MFs-Rul). Meanwhile, another HP-Rul is opened and hence triggers the next cycle of hybridization and digestion process; thus, multiple MFs-Rul are generated. MFs-Rul diffuse easily to the ITO electrode because of small electrostatic repulsion, resulting in an evident signal enhancement. Under the optimal conditions, the ΔECL has a linear relationship with the logarithm of NF-κB p50 concentration ranging from 0.1 to 500 pM. The detection limit is 29 fM (S/N = 3). The sensing platform has been successfully applied to detect NF-κB p50 in cell lysates and also demonstrated to work well for NF-κB p50 inhibitor detection, exhibiting great potential in the diagnosis of disease and drug discovery.

An eco-friendly MIP-solid surface fluorescence immunosensor for detection of CA 19-9 tumor marker using Ni nanocluster as an emitter labels

In the present study, an eco-friendly solid surface fluorescence immunosensor was fabricated for the ultra-selective and sensitive determination of CA 19-9 antigen based on polydopamine (PDA) molecular imprinted polymer (MIP) as an antibody substitution and Ni nanoclusters (Ni NCs) as the fluorescent signal probe. Here, the uniform MIP film for CA 19-9 antigen was established by electropolymerization of DA and target antigen on the surface of ITO electrode. When the imprinted cavities were occupied by CA 19-9 antigen and Ni NCs-Ab, respectively, the fluorescence emission of Ni NCs on the MIP-modified electrode surface was increased. Actually, MIP has been used in immunoassays as antibody substitute. Under optimized experimental conditions, taking advantage of both MIP-FL assays, the proposed immunosensor demonstrated a good analytical performance for the CA 19-9 antigen detection in an excellent linear range from 1 pg mL−1 to 48 ng mL−1 with detection limit of 0.13 pg mL−1 (S/N = 3). The application of the proposed MIP-FL immunosensor for detection of CA 19-9 antigen in human serum samples was evaluated, and the obtained results were found to be in acceptable agreement with those obtained with an ELISA assay as standard method. The developed fluorescence immunosensor demonstrated high specificity and can provide a simple, sensitive and reliable approach for the ultra-trace detection of other tumor markers in clinical monitoring.

Diaphorase-Catalyzed Formation of a Formazan Precipitate and Its Electrodissolution for Sensitive Affinity Biosensors.

Catalytic precipitation and subsequent electrochemical oxidation or reduction of a redox-active precipitate has been widely used in electrochemical biosensors. However, such biosensors often do not allow for low detection limits due to a low rate of precipitation, nonspecific precipitation, loose binding of the precipitate to the electrode surface, and insulating behavior of the precipitate within a normal potential window. Here, we report an ultrasensitive electrochemical immunosensor for parathyroid hormone (PTH) detection based on DT-diaphorase (DT-D)-catalyzed formation of an organic precipitate and electrochemical oxidation of the precipitate. In the present study we found that DT-D can be used as a catalytic label in precipitation-based affinity biosensors because DT-D catalyzes fast reduction of 3-(4,-5-dimethylthiazo-2-yl)-2,5-diphenyltetrazolium bromide (MTT) to MTT-formazan precipitate; the MTT reduction does not occur in the absence of DT-D; and a high electrochemical signal is obtained at low potentials during electrodissolution of MTT-formazan precipitate. The immunosensor is fabricated using a silane copolymer-modified ITO electrode surface that is suitable for both efficient and strong adsorption of MTT-formazan precipitate. When the enzymatic MTT-formazan precipitation and subsequent MTT-formazan electrodissolution is applied to a sandwich-type immunosensor, PTH can be detected over a wide range of concentrations with a very low detection limit (∼1 pg/mL) in artificial serum. The measured concentrations of PTH in clinical serum samples showed high similarity with those obtained using a commercial instrument.

Photoelectrochemical assay for DNA hydroxymethylation determination based on the inhibited photoactivity of black TiO2 nanosphere by ZnO.

A photoelectrochemical method was proposed for DNA hydroxymethylation determination using black TiO2 (B-TiO2) nanosphere as photoactive material and ZnO as photoactivity inhibitor. After hydroxymethylated DNA (5hmC-DNA) was captured on the probe modified B-TiO2/ITO electrode surface through hybridization, a glycosyl can be then transferred from uridine diphosphoglucose to 5hmC-DNA and formed a covalent structure with -CH2OH in the presence of T4 β-glucosyltransferase (β-GT). Afterwards, based on a series of covalent reaction, amino functionalized ZnO nanoparticles are further immobilized to the surface of the electrode. Due to the capacity to expend the irradiation light and the photogenerated electron of electron donor, the modified ZnO nanoparticles can result in a decreased photocurrent. The developed method shows wide linear ranges from 0.05-200nM for hydroxymethylated DNA and 1-220 unit·mL-1 for T4-β-glucosyltransferase. The corresponding determination limits were 0.013nM and 0.24 unit·mL-1, respectively. The enzyme activity inhibited by 4-phenylimidazole was evaluated. This photoelectrochemical method shows high specificity for 5hmC-DNA (compared to 5fC, 5mC, m6A, control) and β-GT (compared to β-AGT, UGT2B7), and shows excellent stability for testing 5hmC (RSD = 2.75%). Graphical abstractSchematic representation of photoelectrochemical method for DNA hydroxymethylation and β-glucosyltransferase detection based on the glycosylation reaction of -CH2OH in 5-hydroxymethylcytosine and the inhibition activity of ZnO to the photoactivity of black TiO2 nanospheres.

Label-free and immobilization-free electrochemiluminescent sensing platform for highly sensitive detection of As(III) by combining target-induced strand displacement amplification with polydopamine nanospheres

Strand displacement amplification (SDA) is a classic isothermal amplification technique, which usually requires one primer and one template. Here, we integrated the primer and the template to design a hairpin DNA. Using polydopamine nanospheres (PDANS) as a reversible and nonspecific inhibitor, an immobilization-free and label-free ECL sensor was fabricated. Without As(III), hairpin DNA is constrained by PDANS, and SDA process is inhibited. Ru(phen)32+, as ECL probe, can diffuse to the negatively charged ITO electrode surface to bring strong ECL response. While the presence of As(III) released the hairpin DNA, and triggered the SDA process with the help of polymerase and nicking endonuclease to generate lots of dsDNA, which interacted with Ru(phen)32+ to form the complex of dsDNA-Ru(phen)32+. The complex is difficult to approach the ITO electrode surface owing to the electrostatic repulsion, resulting in low ECL response. As a consequence, the detection limit of 1.2 × 10−3 ppb for As(III) can be achieved. Meanwhile, it is also applied to assay As(III) in flos sophorae. This strategy not only avoided the adjustment of primer-template ratio and improved amplification efficiency, but also reduced the treatment of the electrode and the immobilization of probe on the electrode. It is hopeful that this method was applied to assay food contaminants, environmental pollutions.

A novel ultrasensitive sandwich-type photoelectrochemical immunoassay for PSA detection based on dual inhibition effect of Au/MWCNTs nanohybrids on N-GQDs/CdS QDs dual sensitized urchin-like TiO2

Abstracts An ultrasensitive sandwich-type photoelectrochemical immunosensor (PEC) was designed successfully for the quantify detection of prostate specific antigen (PSA). Here, urchin-like TiO2, which was dual sensitized by N-doped graphene quantum dots (N-GQDs) and CdS quantum dots (QDs), were fixed on the surface of ITO electrode and produced a significant photocurrent signal. The TiO2/N-GQDs/CdS QDs composite was not only could use as an excellent photoactive substrate but also could provide abundant functional group to immobilized PSA antibodies (Ab1). Using Au/MWCNTs nanohybrids as the label of the secondary antibody (Ab2), Au nanoparticles (NPs) and CdS QDs generated excition-plasmon interactions, and Au NPs produced surface plasmon resonance under photoexcitation. Meanwhile along with the energy transfer process, the photocurrent was inhibited which results in an increase in the sensitivity of the immunosensor. In addition, the loading amount of the labeled Ab2 could be increased due to the large surface area of Au/MWCNTs, the photocurrent signal was further reduced after the specific immune recognition. Under the optimal performance, the sandwich immunosensor proved an ideal linear relationship ranging from 0.1 pg/mL to 50 ng/mL and the detection limit was 6.16 fg/mL with good sensitivity and stability, which provided a promising PEC platform and valuable referential idea for the detection of other trace tumor markers.

A novel electrochemical immunosensor based on disposable ITO-PET electrodes for sensitive detection of PAK 2 antigen

In the present work, we have developed a novel electrochemical immunosensor based on modified disposable ITO-PET (indium tin oxide - polyethylene terephthalate) electrodes for PAK-2 (p21-activated kinase 2) early detection. An ITO-PET electrode surface was modified with 3-cyanopropyl trimethoxysilane (3-CPTMS), which formed self-assembled monolayers (SAMs). PAK2 immunosensing was performed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) techniques, square wave voltammetry (SWV) and a single frequency impedance (SFI) technique utilized for specific interaction between the anti-PAK2 and PAK2 antigen. Further, the morphological characterization of each ITO electrode surface was observed by scanning electron microscopy (SEM). All parameters such as 3-CPTMS concentration, antibody concentration and antibody incubation time were optimized. Analytical characteristics of the proposed immunosensor such as linear determination range, repeatability, reproducibility, regeneration, storage life and surface coverage of immunosensors were determined. The PAK2 electrochemical immunosensor performed flawlessly with a wide determination range (from 0.05 pg mL−1 to 2.5 pg mL−1) and low limits of detection (0.0252 pg mL−1) and of quantification (0.0842 pg mL−1). The artificial and human serum samples were tested to verify the viability of the proposed immunosensor.

A comparison between LP(GMA) and CLP(GMA) polymer composites as an immobilization matrix for biosensing applications: A model immunosensor for IL 1α

A comparative study was made by using two matrices (Linear poly(glycidyl methacrylate) (GMA) polymer (LP(GMA)) and carbon black-polyvinylidene fluoride (PVDF)-LP(GMA) composite CLP(GMA)) as immobilization platforms for anti-IL 1α antibody on the development of impedimetric immunosensor for IL 1α biomarker determination. These materials were spin coated onto the clean ITO electrode surface separately and used for IL 1α immunosensor fabrication. Carbon black is utilized as a conductive material and has been employed over the last few decades for electrochemical biosensors development. The using of CLP(GMA) composite as an interface material shows fast electron transfer, when compared to LP(GMA) modified ITO electrode. This comparative study investigated the efficacy of carbon black for impedimetric biosensing. Anti-IL 1α antibodies were utilized as bioreceptors and bound to epoxy groups of GMA polymer. For electrochemical characterizations, Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and Single Frequency Impedance methods were employed. Furthermore, to follow the antibody attachment on the modified ITO substrates, Fourier Transform Infrared Spectroscopy and Raman spectral techniques were utilized. The morphological characterizations of immunosensor construction stages were carried out by Scanning Electron Microscopy and Atomic Force Microscopy analyses. The sensitive and label-free technique of EIS was used for quantification of IL 1α concentration. Under optimum experimental conditions, the immunosensor had a good linear relationship between impedance values and the IL 1α concentrations ranging from 0.01 to 2 pg/mL and from 0.01 to 3 pg/mL for LP(GMA) and CLP(GMA) modified ITO electrodes, respectively. The results confirmed that CLP(GMA) used in the preparation of the immunosensor illustrated improvements in immunosensor performance, comparing to the LP(GMA) modified immunosensor. Additionally, the immunosensor was successfully applied to evaluate human serum and saliva samples. The obtained results from these samples illustrated the feasibility of the immunosensor for clinical diagnosis in complex biological samples. Also, a simple and low-cost approach was attempted for development of immunosensor with remarkable performance characteristics.