Electrophoresis-driven AIE luminogens encapsulated within silica isoporous membrane for acid vapor sensing

Acid vapors emitted by chemical industries pose an increasing threat to public health. The development of a cost-effective sensor for the on-site and real-time monitoring of environmental acid vapor is of great significance. Aggregation-induced emission (AIE) luminogens overcome the aggregation-caused quenching effect and exhibit intense fluorescence when supported in the solid matrices. Silica isoporous membrane (SIM), characterized by vertically ordered nanochannels, holds great promise as a platform for encapsulating AIE luminogens and enabling gas sensing applications. The SIM containing surfactant micelles was prepared on an ITO electrode to obtain the M-SIM/ITO, and Tetrakis(4-carboxyphenyl)ethylene (TCPE) was employed as the investigated AIE luminogen. Upon application of positive potential, the negatively charged TCPE molecules were driven into the vertically ordered nanochannels, resulting in observable AIE fluorescence. By investigating the electrophoresis conditions such as TCPE charge, nanochannel microenvironment, and driving electric field, the AIE mechanism within the nanochannels was elucidated. The fluorescence of TCPE@M-SIM/ITO exhibited high sensitivity towards acid vapor and displayed reversible changes during the absorption and desorption processes. This behavior can be attributed to the SIM's strong absorption capability towards acid vapor as well as the reversible conversion of acid vapor on TCPE aggregates. This work presented an innovative methodology for studying luminophores within an orderly nanoconfined space, leading to a new perspective on the AIE mechanism.

Electrochemical/Electrochemiluminescence Sensors Based on Vertically-Ordered Mesoporous Silica Films for Biomedical Analytical Applications

Vertically-ordered mesoporous silica films (VMSF, also named as silica isoporous membranes) have shown tremendous potential in the field of electroanalytical sensors due to their unique features in terms of controllable and ultrasmall nanopores, high molecular selectivity and permeability, and mechanical stability. This review will present the recent progress on the biomedical analytical applications of VMSF, focusing on the small biomolecules, diseases-related biomarkers, drugs and cancer cells. Finally, conclusions with recent developments and future perspective of VMSF in the relevant fields will be envisioned.

Electrolytic growth of phenyl-modified silica isoporous membrane for non-polar extraction and electrochemical detection of pentachloronitrobenzene

A phenyl-modified silica isoporous membrane (Ph-SIM) was prepared on the indium-tin-oxide (ITO) electrode using the electrochemically assisted self-assembly (EASA) method. The resulting Ph-SIM preserved vertically ordered nanochannels while exhibiting outstanding hydrophobicity due to the incorporation of phenyl groups within the nanochannels. As a result, the Ph-SIM/ITO sensor exhibited a remarkable affinity for PCNB extraction through hydrophobic interactions, leading to high detection sensitivity. The electrochemical response showed a linear enhancement with the logarithmic concentration of PCNB ranging from 0.1 to 20.0 µM, and the limit of detection was 4.64 nM. Practical results demonstrated that the Ph-SIM/ITO sensor possessed good anti-fouling capability and robust stability, making it a promising candidate for portable detection of non-polar contaminants.

Electrophoretic deposition of Ru(bpy)32+ in vertically-ordered silica nanochannels: A solid-state electrochemiluminescence sensor for prolidase assay

Prolidase (PLD) plays a crucial role as a dipeptidase in various physiological processes, specifically involved in the cleavage of proline-containing dipeptides for efficient recycling of proline. The accurate determination of PLD activity holds significant importance in clinical diagnosis. Herein, a solid-state electrochemiluminescence (ECL) biosensor was developed to address the urgent need for PLD assay. The Ru(bpy)32+ was electrophoretically deposited within the nanochannels of vertically-ordered mesoporous silica film (VMSF) on indium tin oxide (ITO) electrodes. The Ru(bpy)32+-deposited VMSF/ITO (Ru-VMSF/ITO) exhibited a remarkable ECL response towards proline, attributed to the enhanced concentration of the reactants and improved electron transfer resulting from the nanoconfinement effect. As PLD specifically enzymolyzed the Gly-Pro dipeptide to release proline, a proline-mediated biosensor was developed for PLD assay. Increased PLD activity led to enhanced release of proline into the porous solid-state ECL sensors, resulting in a more robust ECL signal. There was a linear relationship between ΔECL intensity and logarithmic concentration of PLD in the range of 10-10000 U/L, with a detection limit of 1.98 U/L. Practical tests demonstrated the reliability and convenience of the proposed bioassay, making it suitable for widespread application in PLD assays.

Composite Silica-Based Films as Platforms for Electrochemical Sensors

Sol-gel-derived silica thin films generated onto electrode surfaces in the form of organic-inorganic hybrid coatings or other composite layers have found tremendous interest for being used as platforms for the development of electrochemical sensors and biosensors. After a brief description of the strategies applied to prepare such materials, and their interest as electrode modifier, this review will summarize the major advances made so far with composite silica-based films in electroanalysis. It will primarily focus on electrochemical sensors involving both non-ordered composite films and vertically oriented mesoporous membranes, the biosensors exploiting the concept of sol-gel bioencapsulation on electrode, the spectroelectrochemical sensors, and some others.

T Cell Antigen Recognition and Discrimination by Electrochemiluminescence Imaging

Adoptive T lymphocyte (T cell) transfer and tumour-specific peptide vaccines are innovative cancer therapies. An accurate assessment of the specific reactivity of T cell receptors (TCRs) to tumour antigens is required because of the high heterogeneity of tumour cells and the immunosuppressive tumour microenvironment. In this study, we report a label-free electrochemiluminescence (ECL) imaging approach for recognising and discriminating between TCRs and tumour-specific antigens by imaging the immune synapses of T cells. Various T cell stimuli, including agonistic antibodies, auxiliary molecules, and tumour-specific antigens, were modified on the electrode's surface to allow for their interaction with T cells bearing different TCRs. The formation of immune synapses activated by specific stimuli produced a negative (shadow) ECL image, from which T cell antigen recognition and discrimination were evaluated by analysing the spreading area and the recognition intensity of T cells. This approach provides an easy way to assess TCR-antigen specificity and screen both of them for immunotherapies.

Electrochemical Sensor Nanoarchitectonics for Sensitive Detection of Uric Acid in Human Whole Blood Based on Screen-Printed Carbon Electrode Equipped with Vertically-Ordered Mesoporous Silica-Nanochannel Film

Screen-printed carbon electrodes (SPCEs) bear great potential in the detection of biomarker in clinical samples with low sample consumption. However, modification of electrode surfaces to improve the anti-interference ability and sensitivity is highly desirable for direct electroanalysis of whole blood samples. Here, a reliable and miniaturized electrochemical sensor is demonstrated based on SPCE equipped with vertically-ordered mesoporous silica-nanochannel film (VMSF). To achieve stable binding of VMSF and improve the electrocatalytic performance, electrochemically reduced graphene oxide (ErGO) is applied as a conductive adhesion layer, that is in situ reduced from GO nanosheets during fast growth (less than 10 s) of amino groups modified VMSF (NH2-VMSF) using electrochemically assisted self-assembly (EASA). In comparison with bare SPCE, NH2-VMSF/ErGO/SPCE exhibits decreased oxidation potential of uric acid (UA) by 147 mV owing to significant electrocatalytic ability of ErGO. The dual signal amplification based on electrocatalysis of ErGO and enrichment of nanochannels leads to enhanced peak current by 3.9 times. Thus, the developed NH2-VMSF/ErGO/SPCE sensor enables sensitive detection of UA in the range from 0.5 μM to 180 μM with a low limit of detection (LOD, 129 nM, S/N = 3). Owing to good anti-fouling ability and high selectivity of the sensor, direct and rapid detection of UA in human whole blood is realized with very low sample consumption (50 μL).

Ultrasensitive Immunosensor for Prostate-Specific Antigen Based on Enhanced Electrochemiluminescence by Vertically Ordered Mesoporous Silica-Nanochannel Film

Ultrasensitive and specific detection of prostate-specific antigen (PSA) in complex biological samples is crucial for early diagnosis and treatment of prostate-related diseases. Immunoassay with a simple sensing interface and ultrahigh sensitivity is highly desirable. Herein, a novel electroluminescence (ECL) immunosensing platform is demonstrated based on the equipment of vertically ordered mesoporous silica-nanochannel films (VMSFs) with PSA antibody, which is able to realize ultrasensitive detection of PSA in human serum. Through the electrochemically assisted self-assembly (EASA) method, the VMSF is easily grown on an indium tin oxide (ITO) electrode in a few seconds. Owing to a large surface area and the negatively charged surface, VMSF nanochannels display strong electrostatic attraction to the positively charged ECL luminophores (tris(2,2-bipyridyl) dichlororuthenium (II), (Ru(bpy)₃²⁺), leading to two orders-of-magnitude enhancement of ECL emission compared with that of the bare ITO electrode. The outer surface of the VMSF is functionalized with reactive epoxy groups, which further allows covalent attachment of PSA antibody (Ab) on the entry of nanochannels. As the combination of PSA with Ab decreases the ECL signal by hindering the mass transfer of ECL luminophores and coreactant, the developed immunosensor can achieve ultrasensitive detection of PSA ranging from 1 pg ml⁻¹ to 100 ng ml⁻¹ with a limit of detection (LOD) of 0.1 pg ml⁻¹. Considering the antifouling ability of the VMSF, sensitive detection of PSA in human serum is also realized. The proposed nanochannel-based immunosensor may open up a new way for the facile development of the universal immunosensing platform for rapid and ultrasensitive detection of disease markers.

Three-dimensional macroscopic graphene supported vertically-ordered mesoporous silica-nanochannel film for direct and ultrasensitive detection of uric acid in serum

Direct, rapid and sensitive detection of physiologically-relevant active small molecules (ASMs) in complex biological samples is highly desirable. Herein, we present an electrochemical sensing platform by combining three-dimensional macroscopic graphene (3DG) and vertically-ordered mesoporous silica-nanochannel film (VMSF), which is able to directly detect ASMs in complex samples with high sensitivity and no need of tedious pretreatment. Free-standing and macroscopic 3DG serves as the supporting electrode and O₂-plasma treatment is proposed as a simple and green approach to improve its hydrophilicity and electrochemical activity. The plasma-treated 3DG (pl-3DG) is suitable for stable modification of VMSF using electrochemically assisted self-assembly (EASA) method, conferring the electrode (VMSF/pl-3DG) with excellent anti-fouling properties. As the proof-of-concept demonstration, VMSF/pl-3DG sensor exhibits fast and ultrasensitive determination of uric acid (UA) with ultralow limit of detection (LOD, 23 nM) owing to high active surface, unhindered mass transfer, good electrical transfer of 3DG and signal amplification of VMSF nanochannel. Direct determination of UA in biological sample (serum) is also realized without the need of tedious pretreatment.

Silica Nanochannel Array Film Supported by ß-Cyclodextrin-Functionalized Graphene Modified Gold Film Electrode for Sensitive and Direct Electroanalysis of Acetaminophen

Convenient and sensitive detection of active analytes in complex matrix is crucial in biological, medical, and environmental analysis. Silica nanochannel array film (SNF) equipped electrochemical sensors have shown excellent anti-fouling performance in direct analysis of complex samples. In this work, we demonstrated an electrochemical sensor with anti-fouling performance for highly sensitive detection of acetaminophen (APAP) based on SNF supported by ß-cyclodextrin-graphene (CDG) nanocomposite modified Au film electrode (AuF). Because of their rich surface hydroxyls and 2D lamellar structure, CDG on AuF can serve as the nanoadhesive for compact binding SNF, which can be grown by electrochemical assisted self-assembly method in a few seconds. Attributable to the electrocatalytic property of graphene and the synergistic enrichment from both CD and SNF nanochannels towards analyte, the SNF/CDG/AuF sensor demonstrates sensitive detection of acetaminophen ranged from 0.2 to 50 μM with an ultralow limit-of-detection of 14 nM. Taking advantage of the anti-fouling ability of SNF, the sensor is able to realize accurate and convenient analysis of APAP in commercially available paracetamol tablets.

Polyaniline nanowire arrays generated through oriented mesoporous silica films: effect of pore size and spectroelectrochemical response

Indium-tin oxide electrodes modified with vertically aligned silica nanochannel membranes have been produced by electrochemically assisted self-assembly of cationic surfactants (cetyl- or octadecyl-trimethylammonium bromide) and concomitant polycondensation of the silica precursors (tetraethoxysilane). They exhibited pore diameters in the 2-3 nm range depending on the surfactant used. After surfactant removal, the bottom of mesopores was derivatized with aminophenyl groups via electrografting (i.e., electrochemical reduction of in situ generated aminophenyl monodiazonium salt). These species covalently bonded to the ITO substrate were then exploited to grow polyaniline nanofilaments by electropolymerization of aniline through the nanochannels. Under potentiostatic conditions, the length of polyaniline wires is controllable by tuning the electropolymerization time. From cyclic voltammetry characterization performed either before or after dissolution of the silica template, it appeared that both the polyaniline/silica composite and the free polyaniline nanowire arrays were electroactive, yet with much larger peak currents in the latter case as a result of larger effective surface area offered to the electrolyte solution. At identical electropolymerization time, the amount of deposited polyaniline was larger when using the silica membrane with larger pore diameter. All polyaniline deposits exhibited electrochromic properties. However, the spectroelectrochemical data indicated more complete interconversion between the coloured oxidized form and colourless reduced polyaniline for the arrays of nanofilaments in comparison to bulky films. In addition, the template-free nanowire arrays (i.e., after silica dissolution) were characterized by faster electrochromic behaviour than the polyaniline/silica hybrid, confirming the potential interest of such polyaniline nano-brushes for practical applications.

Vertically Ordered Mesoporous Silica-Nanochannel Film-Equipped Three-Dimensional Macroporous Graphene as Sensitive Electrochemiluminescence Platform

Three-dimensional (3D) electrochemiluminescence (ECL) platform with high sensitivity and good anti-fouling is highly desirable for direct and sensitive analysis of complex samples. Herein, a novel ECL-sensing platform is demonstrated based on the equipment of vertically ordered mesoporous silica-nanochannel films (VMSF) on monolithic and macroporous 3D graphene (3DG). Through electrografting of 3-aminopropyltriethoxysilane (APTES) onto 3DG as molecular glue, VMSF grown by electrochemically assisted self-assembly (EASA) method fully covers 3DG surface and displays high stability. The developed VMSF/APTES/3DG sensor exhibits highly sensitized ECL response of tris(2,2'-bipyridyl) ruthenium (Ru (bpy)3 2+) taking advantages of the unique characteristics of 3DG (high active area and conductivity) and VMSF nanochannels (strong electrostatic enrichment). The VMSF/APTES/3DG sensor is applied to sensitively detect an important environmental pollutant (4-chlorophenol, with limit of detection or LOD of 30.3 nM) in term of its quenching effect (ECL signal-off mode) toward ECL of Ru (bpy)3 2+/tri-n-propylamine (TPrA). The VMSF/APTES/3DG sensor can also sensitively detect the most effective antihistamines chlorpheniramine (with LOD of 430 nM) using ECL signal-on mode because it acts as co-reactant to promote the ECL of Ru (bpy)3 2+. Combined with the excellent antifouling ability of VMSF, the sensor can also realize the analysis of actual environmental (lake water) and pharmaceutical (pharmacy tablet) samples. The proposed 3D ECL sensor may open new avenues to develop highly sensitive ECL-sensing platform.

Vertically oriented mesoporous silica film modified fluorine-doped tin oxide electrode for enhanced electrochemiluminescence detection of lidocaine in serum

Owing to a nanochannel-based enrichment effect and anti-fouling ability, highly ordered and vertically oriented mesoporous silica thin film (VMSF) modified electrodes have demonstrated their great potential in direct and highly sensitive analysis of complex samples. In this work, a VMSF modified fluorine-doped tin oxide (FTO) electrode (VMSF/FTO) is fabricated for enhanced electrochemiluminescence (ECL) analysis of lidocaine in serum. VMSF with good integrity and mechanical stability can be rapidly and conveniently grown on FTO in a few seconds at room temperature using an electrochemically assisted self-assembly (EASA) method. Due to the strong electrostatic attraction between the cationic ECL probe and negatively charged nanochannel, the VMSF/FTO electrode shows significant enrichment of tris(2,2-bipyridine) ruthenium(ii) (Ru(bpy)₃ ²⁺), leading to ∼10 times enhancement of its ECL signal in comparison to the bare FTO electrode. Lidocaine, an anesthetic and antiarrhythmic drug, can act as the co-reactant of Ru(bpy)₃ ²⁺ and promote its ECL signal. Sensitive ECL detection of lidocaine is achieved by the sensor in a wide linear range from 10 nM to 50 μM with a low limit-of-detection (LOD) of 8 nM. Combined with the antifouling ability of VMSF, the VMSF/FTO electrode also realizes the accurate and rapid analysis of lidocaine in real serum samples.

Tailoring molecular permeability of vertically-ordered mesoporous silica-nanochannel films on graphene for selectively enhanced determination of dihydroxybenzene isomers in environmental water samples

Herein we demonstrate a simple and rapid electrochemical method for selectively enhanced determination of catechol (CC) or hydroquinone (HQ) isomers in environmental water samples by tailoring the molecular permeability of vertically-ordered mesoporous silica-nanochannel films on electrochemically reduced graphene oxide (VMSF/ErGO). Such VMSF/ErGO composite film was fabricated on the gold electrode (AuE) surface using electrochemically assisted self-assembly approach. The as-prepared electrodes with surfactant micelles (SM) template inside silica nanochannels, designed as SM/VMSF/ErGO/AuE, possess hydrophobic hydrocarbon cores and show preferential response to CC via hydrophobic effect. After removing SM from silica nanochannels, the obtained VMSF/ErGO/AuE displays more sensitive response to HQ, which is due to the hydrogen bond effect between the silanol groups of silica walls and HQ. Given the potential-resolved and high electrocatalytic ability of ErGO, and molecular permeability and anti-fouling ability of VMSF, these two present sensors could detect CC and HQ in lake water with a low limit of detection (18 nM for CC and 16 nM for HQ), and a high sensitivity (0.33 μA/μM for CC and 0.37 μA/μM for HQ), without complicated sample pretreatment. Moreover, the proposed sensors provide a convenient, rapid and economic way for direct analysis of environmental water samples, exhibiting excellent long-term stability.

pH-Responsive Ultrathin Nanoporous SiO2 Films for Selective Ion Permeation

Ultrathin nanoporous (NP) films are an emerging field for selective and effective ion/molecular separation and electrochemical sensing applications. We describe selective ion permeation in surface-functionalized ultrathin NP SiO₂ films (NP SiO₂-NH₂). The ultrathin NP SiO₂ films with ca. 8 nm thickness were prepared from silsesquioxane-containing blend polymer Langmuir-Blodgett films (nanosheets) using the photo-oxidation method. The porous SiO₂ surface was modified with a pH-responsive amine-containing silane coupling agent. Selective ion permeation was demonstrated under acidic pH conditions (pH ≤ 6) using two equally sized redox probes: negative (Fe(CN)₆^3-/4-) and positive (Ru(NH₃)₆^2+/3+) ions. The current density for Fe(CN)₆^3-/4- decreased as the pH value increased to pH = 6, whereas it increased for Ru(NH₃)₆^2+/3+. Control measurements revealed that the probes can penetrate the pores of nonfunctionalized SiO₂ films irrespective of pH values, indicating that both the size and the surface charge response contributed to selective ion permeation. Results obtained from this study pave the way for new applications in molecular separation and sensing applications based on ultrathin nanoporous films (<10 nm) and tailored surfaces.

Growing vertical aligned mesoporous silica thin film on nanoporous substrate for enhanced degradation, drug delivery and bioactivity

Mesoporous silica thin film has been widely used in various fields, particularly the medical implant coating for drug delivery. However, some drawbacks remain with the films produced by traditional method (evaporation-induced self-assembly, EISA), such as the poor permeability caused by their horizontal aligned mesochannels. In this study, the vertical aligned mesoporous silica thin film (VMSTF) is uniformly grown alongside the walls of titania nanotubes array via a biphase stratification growth method, resulting in a hierarchical two-layered nanotubular structure. Due to the exposure of opened mesopores, VMSTF exhibits more appealing performances, including rapid degradation, efficient small-molecular drug (dexamethasone) loading and release, enhanced early adhesion and osteogenic differentiation of MC3T3-E1 cells. This is the first time successfully depositing VMSTF on nanoporous substrate and our findings suggest that the VMSTF may be a promising candidate for bone implant surface coating to obtain bioactive performances.

A label-free and homogenous electrochemical assay for matrix metalloproteinase 2 activity monitoring in complex samples based on electrodes modified with orderly distributed mesoporous silica films

Herein, a label-free and homogeneous electrochemical strategy for monitoring of matrix metalloproteinase 2 (MMP-2) activity was proposed based on electrodes modified with orderly distributed mesoporous silica films (MSFs). In the absence of target MMP-2, an artificially substrate peptide with positive charge was absorbed on the surface of MSFs by electrostatic interaction, which could prevent electrochemical molecules [Ru(NH₃)₆]Cl₃ from approaching the electrode surface. When the substrate peptide was hydrolyzed by target MMP-2, [Ru(NH₃)₆]Cl₃ could arrive to the electrode surface and lead to the increase of electrochemical signal. This assay showed considerable sensitivity to target MMP-2, which could measure it down to 0.98 ng. mL^-1. Meanwhile, a satisfied response to the inhibitor of MMP-2 was also achieved (IC-50 value = 1.68 μM). Significantly, it displayed satisfactory performances in the complicated biological samples including cell lysates and human serum. Taking advantages of the anti-fouling ability in biological complex samples of MSFs and the high efficiency of homogeneous sensing, this assay realized the electrochemical detection of MMP-2 with accuracy and sensitivity, which exhibited significant potential in clinical biomedicine and biological analysis of cancer-related protease.

Rapid and sensitive determination of doxorubicin in human whole blood by vertically-ordered mesoporous silica film modified electrochemically pretreated glassy carbon electrodes

Direct and accurate detection of doxorubicin (DOX) in unprocessed human whole blood is of vital importance in medical diagnosis and monitoring. In this work, we demonstrate the utilization of electrochemically pretreated glassy carbon electrodes (p-GCE) modified with vertically-ordered mesoporous silica films (VMSF) for rapid and sensitive electrochemical detection of DOX. The electrochemically pretreated process is a simple, cost-effective and environmentally friendly approach for improving interface catalytic properties and introducing oxygen-containing groups into the GCE surface, which could be suitable for stably growing VMSF without any adhesive layer simultaneously retaining the underlying electrode activity. Benefiting from the highly sensitive electrode substrate of p-GCE and electrostatic preconcentration effect of VMSF, the present VMSF/p-GCE sensor was able to determine DOX with an ultrahigh sensitivity (23.94 μA μM^-1) and a relatively low limit of detection (0.2 nM) and a rather wide linear range (0.5 nM to 23 μM). Furthermore, direct and reliable electrochemical detection of DOX in human whole blood without complicated sample pretreatments was achieved owing to the excellent anti-fouling and anti-interference ability of VMSF.

Integration of vertically-ordered mesoporous silica-nanochannel film with electro-activated glassy carbon electrode for improved electroanalysis in complex samples

Vertically-ordered mesoporous silica-nanochannel films (VMSF) with highly ordered nanochannels, uniform and adjustable pore size, ultra-thin thickness, and high porosity, have attracted considerable attention in analysis, molecular separation, catalysis, and nanomaterial synthesis. However, their widespread applications in practical electrochemical sensing are largely limited by the poor adhesion to common electrode materials, especially the lack of highly active substrate electrode to equip mechanically stable VMSF. Herein, we report a facile strategy to fabricate VMSF on widely used sensing electrodes without the use of any chemical adhesive for developing superior VMSF based electrochemical sensors. We demonstrate that simple electrochemical polarization (anodic polarization and subsequent cathodic reduction) to activate glassy carbon electrode (GCE) can generate a suitable surface environment allowing direct growth of stable VMSF on such pre-activated GCE (p-GCE) via electrochemically assisted self-assembly (EASA). Compared to traditional VMSF electrodes with ITO or organosilane grafted GCE as substrate, the developed VMSF/p-GCE exhibits much higher electrochemical response to four redox biomarkers (norepinephrine, dopamine, tryptophan, and uric acid). In-depth insights on mechanisms of the high electrochemical activity and incorporation stability of VMSF/p-GCE are made. We further demonstrate the VMSF/p-GCE can be employed to detect dopamine in real serum samples with exceptional sensitivity, low detection potential, as well as superior anti-interference and anti-fouling performance. In addition, high selectivity is realized as the common co-existing interference substances (ascorbic acid-AA and uric acid-UA) do not interfere with the detection.

Signal amplification by electro-oligomerisation for improved isoproturon detection

A novel concept is introduced for signal amplification in electrochemical sensing: the electro-oligomerisation stripping voltammetry, which has been applied here to the improved detection of the isoproturon herbicide in spring waters as a proof-of-principle. It involves a potentiostatic accumulation step onto a glassy carbon electrode (at +1.5 V vs Ag/AgCl reference electrode for 300 s) leading to the formation of an oligomeric film, which is then detected by cathodic stripping square wave voltammetry (SWV). The presence and composition of the film are confirmed by confocal Raman spectroscopy. Its characterisation by cyclic voltammetry demonstrates the reversible nature of the electrodeposited material, confirming its interest for sensitive detection by SWV. Adding a mesoporous silica membrane with vertically oriented nanochannels further enhances the sensitivity of the sensor, exhibiting a linear response in the 10-100 μM concentration range. This effect was even more interesting for real media analysis thanks to the permselective properties of such nanoporous coating in rejecting interferences and/or surface fouling agents. The method should be applicable to other analytes that are usually not detectable by conventional accumulation/stripping voltammetry.

Nanoporous Thin Films Formed from Photocleavable Diblock Copolymers on Gold Substrates Modified with Thiolate Self-Assembled Monolayers

Nanoporous thin films formed on electrodes are considered functional elements of electrochemical sensing systems, thus motivating methods for their development. We report a preparative strategy detailing the effects of surface modification of gold substrates with thiolate self-assembled monolayers (SAMs) on the properties of nanoporous thin films derived from polystyrene-block-poly(ethylene oxide) having a photocleavable o-nitrobenzyl ester junction (PS-hν-PEO). Two PS-hν-PEO having similar PEO volume fractions (≈0.2) but different molecular weights (10 and 23 kg/mol) were used to prepare films (30-100 nm thick) spin-cast on gold substrates unmodified and modified with cysteamine, thioctic acid, and 6-hydroxy-1-hexanethiol SAMs. Solvent vapor annealing followed by PEO removal led to the formation of nanopores with average diameters of 12 and 19 nm from the smaller and larger PS-hν-PEO, respectively. Cyclic voltammograms of 1,1'-ferrocenedimethanol showed that nanoporous films on cysteamine SAMs afforded nanopores reaching the underlying substrates at higher density than those on the other substrates. This result was attributed to balanced affinity of the cysteamine SAM surface with PS and PEO, which enhanced the vertical orientation of PEO microdomains. The generation of carboxyl groups associated with the photocleavage reaction was revealed by pH-dependent changes in the voltammogram of Fe(CN)₆^3- that reflected electrostatic effects regulated by the protonation state of the carboxyl groups. The SAMs underneath the nanoporous films could be replaced by treatment with a thiol solution, as verified by voltammograms of l-ascorbic acid. These results suggest that thiolate SAM modification provides a simple means to control the interfacial orientation of PEO microdomains in thin PS-hν-PEO films.

Quantum Dots with Highly Efficient, Stable, and Multicolor Electrochemiluminescence

Outstanding photoluminescence (PL) and electroluminescence properties of quantum dots (QDs) promise possibilities for them to meet challenging expectations of electrochemiluminescence (ECL), which at present relies on inefficient and spectral-irresolvable emitters based on transition-metal complexes (such as Ru(bpy)3 2+). However, ECL is reported to be extremely sensitive to the surface traps on the QDs likely because of the spatially and temporally separated electrochemical charge injections. Results here reveal that, by engineering the interior inorganic structure (CdSe/CdS/ZnS core/shell/shell structure) and inorganic-organic interface using new synthetic methods, the trap-insensitive QDs with near-unity PL quantum yield and monoexponential PL decay dynamics in water generated narrow band-edge ECL with efficiencies about six orders of magnitude higher than that of the standard Ru(bpy)3 2+. The band-edge and spectrally resolved ECL from CdSe/CdS/ZnS core/shell/shell QDs demonstrated a new readout scheme using electrochemical potential. Excellent ECL performance of QDs uncovered here offer opportunities to realize the full potential of ECL for biomedical detection and diagnosis.

Fabrication of a mesoporous silica film based optical waveguide sensor for detection of small molecules

In this paper, a thick mesoporous silica film (MSF) (more than 700 nm) was fabricated via the two-step enhancing Stöber solution growth approach (ESSGA). According to the optimization based on the transfer matrix method, a thicker MSF sensor has higher waveguide index sensitivity and is more suitable for the adsorbent detection, while a thinner MSF sensor has higher covered medium index sensitivity and is more appropriate for non-adsorbent detection. The covered medium index sensitivity and refractive index resolution of the fabricated MSF optical waveguide sensor were calculated to be 53.18 deg/RIU and ${1.28}\; \times \;{{10}^{ - 6}}\;{\rm RIU}$1.28×10^-6RIU, respectively. For the detection of a small molecule, hexadecyltrimethylammonium bromide was used as a model of a small molecule to verify its sensing property and its limit of detection (LOD) as low as 1.879 nM was obtained. In order to detect heavy metal ions, the MSF was modified with an amino group by the post-grafted method. The response of the resonance angle shift is more sensitive to ${{\rm Pb}^{2 + }}$Pb²⁺ ion than ${{\rm Cu}^{2 + }}$Cu²⁺ ion and both their LODs could reach the nanomolar detection level; those are 17.30 and 6.44 nM, respectively.

Wetting-Controlled Localized Placement of Surface Functionalities within Nanopores

In the context of sensing and transport control, nanopores play an essential role. Designing multifunctional nanopores and placing multiple surface functionalities with nanoscale precision remains challenging. Interface effects together with a combination of different materials are used to obtain local multifunctionalization of nanoscale pores within a model pore system prepared by colloidal templating. Silica inverse colloidal monolayers are first functionalized with a gold layer to create a hybrid porous architecture with two distinct gold nanostructures on the top surface as well as at the pore bottom. Using orthogonal silane- and thiol-based chemistry together with a control of the wetting state allows individual addressing of the different locations within each pore resulting in nanoscale localized functional placement of three different functional units. Ring-opening metathesis polymerization is used for inner silica-pore wall functionalization. The hydrophobized pores create a Cassie-Baxter wetting state with aqueous solutions of thiols, which enables an exclusive functionalization of the outer gold structures. In a third step, an ethanolic solution able to wet the pores is used to self-assemble a thiol-containing initiator at the pore bottom. Subsequent controlled radical polymerization provides functionalization of the pore bottom. It is demonstrated that the combination of orthogonal surface chemistry and controlled wetting states can be used for the localized functionalization of porous materials.

Highly sensitive detection of rutin in pharmaceuticals and human serum using ITO electrodes modified with vertically-ordered mesoporous silica–graphene nanocomposite films

A vertically-ordered silica–graphene nanocomposite film modified transparent ITO electrode was prepared by a one-step electrodeposition method for antifouling detection of rutin in pharmaceuticals and human serum.

Antifouling strategies in advanced electrochemical sensors and biosensors

A review presented recent development of antifouling strategies in electrochemical sensors and biosensors based on the modification methods.

Unraveling Mass and Electron Transfer Kinetics at Silica Nanochannel Membrane Modified Electrodes by Scanning Electrochemical Microscopy

An in-depth understanding of kinetic processes convoluting mass and charge transfer at nanoporous membrane modified electrodes is crucial for developing high-performance electrochemical sensors. In this work, we propose a theoretical model to unravel mass (k_m) and electron transfer rate (k_f) from the apparent electrochemical rate constant (k_app) at silica nanoporous membrane (SNM) modified indium tin oxide (ITO) electrodes (designated as SNM/ITO for simplicity). Using scanning electrochemical microscopy (SECM), the k_app of charged redox species was first determined at the SNM/ITO in the absence and presence of surfactant micelles inside SNM. On the basis of the theory, in the presence of micelles inside SNM, k_m equals zero for all charged probes (Ru(NH₃)₆²⁺, Ru(CN)₆^3-, and FcMeOH⁺), thus the SNM behaves as an insulating barrier and the overall electrode reactivity is dominated by the permeability of SNM. After excluding micelles from SNM, the k_m of Ru(CN)₆^3-/4- is strongly dependent on the KCl concentration in the solution, decreasing from 0.23/0.15 mm s^-1 to almost zero upon decreasing the KCl concentration from 1.0 to 0.01 M. In contrast, k_m increases from 1.33 to 2.4 mm s^-1 for Ru(NH₃)₆²⁺ and from 0.18 to 0.33 mm s^-1 for FcMeOH⁺, which are comparable to the electron transfer rate at the underlying ITO electrode surface (0.8 and 0.35 mm s^-1). In these cases, both mass and electron transfer processes are important in determining the overall redox activity of SNM/ITO electrodes. The methodology reported in this work can provide a quantitative way of unraveling these processes and their respective contributions.

Fabrication and in situ functionalisation of mesoporous silica films by the physical entrapment of functional and responsive block copolymer structuring agents

Stimuli-responsive mesoporous silica films were prepared by evaporation-induced self-assembly through the physical entrapment of a functional block copolymer structuring agent, which simultaneously serves to functionalise the mesopore. These polymer-silica hybrid materials exhibit remarkable ionic permselectivity under highly filled conditions, and offer the potential for local polymer functionalisation for enhanced and tunable ionic permselectivity. This innovative and simple approach for the in situ functionalisation of mesoporous silica has the potential to improve how we approach the design of complex architectures at the nanoscale for enhanced transport, and is thus relevant for a variety of technologies based on molecular transport in nanoscale pores including separation, sensing, catalysis, and energy conversion.

Mesoporous Silica-Based Materials for Electronics-Oriented Applications

Electronics, and nanoelectronics in particular, represent one of the most promising branches of technology. The search for novel and more efficient materials seems to be natural here. Thus far, silicon-based devices have been monopolizing this domain. Indeed, it is justified since it allows for significant miniaturization of electronic elements by their densification in integrated circuits. Nevertheless, silicon has some restrictions. Since this material is applied in the bulk form, the miniaturization limit seems to be already reached. Moreover, smaller silicon-based elements (mainly processors) need much more energy and generate significantly more heat than their larger counterparts. In our opinion, the future belongs to nanostructured materials where a proper structure is obtained by means of bottom-up nanotechnology. A great example of a material utilizing nanostructuring is mesoporous silica, which, due to its outstanding properties, can find numerous applications in electronic devices. This focused review is devoted to the application of porous silica-based materials in electronics. We guide the reader through the development and most crucial findings of porous silica from its first synthesis in 1992 to the present. The article describes constant struggle of researchers to find better solutions to supercapacitors, lower the k value or redox-active hybrids while maintaining robust mechanical properties. Finally, the last section refers to ultra-modern applications of silica such as molecular artificial neural networks or super-dense magnetic memory storage.

Low-voltage efficient electroosmotic pumps with ultrathin silica nanoporous membrane

In this work, an efficient electroosmotic pump (EOP) based on the ultrathin silica nanoporous membrane (u-SNM), which can drive the motion of fluid under the operating voltage as low as 0.2 V, has been fabricated. Thanks to the ultrathin thickness of u-SNM (∼75 nm), the effective electric field strength across u-SNM could be as high as 8.27 × 10⁵ V m^-1 in 0.4 M KCl when 1.0 V of voltage was applied. The maximum normalized electroosmotic flow (EOF) rate was as high as 172.90 mL/min/cm² /V, which was larger than most of other nanoporous membrane based EOPs. In addition to the ultrathin thickness, the high porosity of this membrane (with a pore density of 4 × 10¹² cm^-2 , corresponding to a porosity of 16.7%) also contribute to such a high EOF rate. Moreover, the EOF rate was found to be proportional to both the applied voltage and the electrolyte concentration. Because of small electrokinetic radius of u-SNM arising from its ultrasmall pore size (ca. 2.3 nm in diameter), the EOF rate increased with increasing the electrolyte concentration and reached the maximum at a concentration of 0.4 M. This dependence was rationalized by the variations of both zeta potential and electrokinetic radius with the electrolyte concentration.

Nanochannel-Confined Graphene Quantum Dots for Ultrasensitive Electrochemical Analysis of Complex Samples

Herein, we present an electrochemical sensing platform based on nanochannel-confined graphene quantum dots (GQDs) that is able to detect a spectrum of small analytes in complex samples with high sensitivity. Vertically ordered mesoporous silica-nanochannel film (VMSF) is decorated on the supporting electrode, conferring the electrode with excellent antifouling and anti-interference properties through steric exclusion and electrostatic repulsion. The synthesized GQDs with different functionalities are confined in the nanochannels of VMSF through electrophoresis, serving as the recognition element and signal amplifier. Without the usual need of tedious pretreatment, ultrasensitive and fast detection of Hg²⁺, Cu²⁺, and Cd²⁺ (with limits of detection (LOD) of 9.8 pM, 8.3 pM, and 4.3 nM, respectively) and dopamine (LOD of 120 nM) in complex food (Hg²⁺-contaminated seafood), environmental (soil-leaching solution), and biological (serum) samples are realized as proof-of-concept demonstrations.

Mesoporous Silica Thin Films for Improved Electrochemical Detection of Paraquat

An electrochemical method was developed for rapid and sensitive detection of the herbicide paraquat in aqueous samples using mesoporous silica thin film modified glassy carbon electrodes (GCE). Vertically aligned mesoporous silica thin films were deposited onto GCE by electrochemically assisted self-assembly (EASA). Cyclic voltammetry revealed effective response to the cationic analyte (while rejecting anions) thanks to the charge selectivity exhibited by the negatively charged mesoporous channels. Square wave voltametry (SWV) was then used to detect paraquat via its one electron reduction process. Influence of various experimental parameters (i.e., pH, electrolyte concentration, and nature of electrolyte anions) on sensitivity was investigated and discussed with respect to the mesopore characteristics and accumulation efficiency, pointing out the key role of charge distribution in such confined spaces on these processes. Calibration plots for paraquat concentration ranging from 10 nM to 10 μM were constructed at mesoporous silica modified GCE which were linear with increasing paraquat concentration, showing dramatically enhanced sensitivity (almost 30 times) as compared to nonmodified electrodes. Finally, real samples from Meuse River (France) spiked with paraquat, without any pretreatment (except filtration), were analyzed by SWV, revealing the possible detection of paraquat at very low concentration (10-50 nM). Limit of detection (LOD) calculated from real sample analysis was found to be 12 nM, which is well below the permissible limits of paraquat in drinking water (40-400 nM) in various countries.

Electrochemical detection of Alzheimer's disease related substances in biofluids by silica nanochannel membrane modified glassy carbon electrodes

Alzheimer's disease (AD) affects middle- and old-age populations, and causes loss of brain weight, degradation of brain functions and memory loss.