Vertically Ordered Mesoporous Silica Film-Assisted Label-Free and Universal Electrochemiluminescence Aptasensor Platform

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.

Screening-Capture-Integrated Electrochemiluminescent Aptasensor Based on Mesoporous Silica Nanochannels for the Ultrasensitive Detection of Deoxynivalenol in Wheat

To prevent the contamination of cereals by mycotoxins, establishing a sensitive and rapid method for the detection of mycotoxins is essential. In this study, a screening-capture-integrated electrochemiluminescence (ECL) aptasensor based on mesoporous silica films (MSFs) was successfully prepared for the ultrasensitive and highly selective detection of deoxynivalenol (DON) in wheat. The narrow nanochannels of MSFs can realize size screening, thereby eliminating the influence of macromolecular substances and providing a pure environment for the signal probe (tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)32+)) to reach the indium tin oxide (ITO) conductive substrate, which significantly improves the anti-interference ability of the screening-capture-integrated ECL sensor. The aptamer (Apt) attached to the surface of the MSFs can specifically capture DON, and the resulting DON-Apt complex has a gated effect on the MSFs, triggering the inhibition of Ru(bpy)32+ in the electrolyte from reaching the ITO surface. Therefore, the ECL intensity of the sensor decreased with increasing DON concentration to achieve a quantitative detection of DON. Under optimized conditions, the linear range of the screening-capture-integrated ECL aptasensor was 0.001-200 μg/kg, and the detection limit was as low as 5.27 × 10-5 μg/kg (S/N = 3). In conclusion, this study developed a screening-capture-integrated ECL aptasensor that combines size screening and specific capture for the detection of DON in wheat, providing a new approach for the early detection of wheat mildew.

Vertically-Ordered Mesoporous Silica Film Based Electrochemical Aptasensor for Highly Sensitive Detection of Alpha-Fetoprotein in Human Serum

Convenient and rapid detection of alpha fetoprotein (AFP) is vital for early diagnosis of hepatocellular carcinoma. In this work, low-cost (0.22 USD for single sensor) and stable (during 6 days) electrochemical aptasensor was developed for highly sensitive and direct detection of AFP in human serum with the assist of vertically-ordered mesoporous silica films (VMSF). VMSF has silanol groups on the surface and regularly ordered nanopores, which could provide binding sites for further functionalization of recognition aptamer and also confer the sensor with excellent anti-biofouling capacity. The sensing mechanism relies on the target AFP-controlled diffusion of Fe(CN)₆^3-/4- redox electrochemical probe through the nanochannels of VMSF. The resulting reduced electrochemical responses are related to the AFP concentration, allowing the linear determination of AFP with a wide dynamic linear range and a low limit of detection. Accuracy and potential of the developed aptasensor were also demonstrated in human serum by standard addition method.

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.

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.

Combining Electrochemiluminescence Detection with Aptamer-Gated Indicator Releasing Mesoporous Nanoparticles Enables ppt Sensitivity for Strip-Based Rapid Tests

The combination of electrogenerated chemiluminescence (ECL) and aptamer‐gated indicator delivering (gAID) magnetic mesoporous silica nanoparticles embedded into glass fibre paper functionalised with poly(ethyleneglycol) and N‐(3‐triethoxysilylpropyl)diethanolamine allowed the development of a rapid test that detects penicillin directly in diluted milk down to 50±9 ppt in <5 min. Covalent attachment of the aptamer “cap” to the silica scaffold enabled pore closure through non‐covalent electrostatic interactions with surface amino groups, while binding of penicillin led to a folding‐up of the aptamer thus releasing the ECL reporter Ru(bpy)₃²⁺ previously loaded into the material and letting it be detected after lateral flow by a smartphone camera upon electrochemical excitation with a screen printed electrode inserted into a 3D‐printed holder. The approach is simple, generic and presents advantages with respect to sensitivity, measurement uncertainty and robustness compared with conventional fluorescence or electrochemical detection, especially for point‐of‐need analyses of challenging matrices and analytes at ultra‐trace levels.

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.

A replacement-type electrochemiluminescent aptasensor for lysozyme based on full-electric modification electrode coupled to silica-coated Ru(bpy)32+/silver nanospheres

This research proposed a replacement-type electrochemiluminescent (ECL) aptasensor for lysozyme (LYZ) detection at trace levels based on a full-electric modification electrode (FEMG) coupled to silica-coated Ru(bpy)₃²⁺/silver nanospheres (Ru/SNs@SiO₂). The multi-walled carbon nanotubes-doped-thionine (MWCNTs/PTn) electropolymerized modified electrode was decorated with electrodeposited gold nanoparticles (GNs) to form the FEMG. Then, the FEMG was utilized as sensing substrates for the immobilization of the anti-lysozyme aptamer (LA); the stability and number of LA attaching onto the FEMG were dramatically increased. The ECL measurement was used to evaluate the hybridization reaction of LA and the Ru/SNs@SiO₂ marked DNA probe, and it was noted as I_a. After the combination of the LA with the LYZ, the target-triggered replacement of the DNA probe was actualized and the ECL measurement descended to I_b. The ECL difference (ΔI_ECL = I_a - I_b) before and after the replacement event was utilized for quantitation of LYZ. As a result, the fabricated aptasensor with great sensitivity and specificity achieved a wide linear range (10 fM-10 pM) and a low limit of detection (5 fM). It obtained satisfactory recovery for the detection of LYZ in human serum, and the results were identified with the LYZ ELISA kit. Therefore, the proposed ECL sensor is expected to become a promising approach in the field of biomolecule detection.

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.

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.

A novel vertical aligned mesoporous silica coated nanohydroxyapatite particle as efficient dexamethasone carrier for potential application in osteogenesis

Bone defect is a common problem and inducing osteoblasts differentiation is the key process for the regenerative repair. Recently, the mesoporous silica (MS) coated nanohydroxyapatite particles nHA (nHA-MS) has shown enhanced intrinsic potency for bone regeneration, whereas whether the osteogenesis potency can be further enhanced after drug delivery has not been investigated. In this study, the nHA-MS was fabricated by a novel biphase stratification growth way. The cytotoxicity in MC3T3-E1 was validated by MTT assay, apoptosis analysis and cell cycle examination. The cell uptake was observed by confocal laser scanning microscope and transmission electron microscope respectively. After adsorption with dexamethasone (DEX), the osteogenic differentiation was determined both in vitro and in vivo. The synthesized nHA-MS showed a core-shell structure that the nanorod-like nHA was coated by a porous MS shell (~5 nm pores diameter, ~50 nm thickness). A dose-dependent cytotoxicity was observed and below 10 µg/ml was a safe concentration. The nHA-MS also showed efficient cell uptake efficiency and more efficient in DEX loading and release. After DEX adsorption, the nanoparticles exhibited enhanced osteogenic induction in MC3T3-E1 and rat calvarial bone defect regeneration. In conclusion, the nHA-MS is a favorable platform for drug delivery to obtain more enhanced osteogenesis capabilities.

Dual-Modular Aptasensor for Detection of Cardiac Troponin I Based on Mesoporous Silica Films by Electrochemiluminescence/Electrochemical Impedance Spectroscopy

A simple, dual-modular aptasensor for accurate determination of cardiac troponin I (cTnI), a sensitive biomarker of acute myocardial infarction, is reported. It has the parallel output of electrochemiluminescence (ECL) and electrochemical impedance spectroscopy (EIS) based on target-gated transportation of signal probes (luminol/H₂O₂ or Fe(CN)₆^3-/4-). The sensing capacity is originated from the amino-functionalized mouth margin of the nanochannels in a vertically oriented mesoporous silica film, which was in situ-grown on indium tin oxide-coated glass. With the linkage of glutaraldehyde to couple the aptamer as a trapper, it brings in the high specific target-gated response toward cTnI as decreased ECL or increased EIS. The concentration of cTnI is measurable by the ECL response within a wide linear range from 0.05 pg mL^-1 to 10 ng mL^-1, as well as the EIS response for a linear range between 0.05 pg mL^-1 and 1 ng mL^-1. Significantly, the self-verification of these two data from ECL and EIS validated each other with a satisfactory linear correlation (R² = 0.999), thereby realizing the more reliable and accurate quantification to avoid false results. The designed strategy is an effective method for detection of cTnI, which is of great potential to apply in clinical detection.

Hydrocolloid-Based Coatings with Nanoparticles and Transglutaminase Crosslinker as Innovative Strategy to Produce Healthier Fried Kobbah

This study addresses the effect of coating solutions on fried kobbah. Coating solutions were made of pectin (PEC) and grass pea flour (GPF), treated or not with transglutaminase (TGase) and nanoparticles (NPs)—namely mesoporous silica NPs (MSN) or chitosan NPs (CH–NPs). Acrylamide content (ACR), water, oil content and color of uncoated (control) and coated kobbah were investigated. Zeta potential, Z-average and in vitro digestion experiments were carried out. Zeta potential of CH–NPs was stable from pH 2.0 to pH 6.0 around + 35 mV but decreasing at pH > 6.0. However, the Z-average of CH–NPs increased by increasing the pH. All coating solutions were prepared at pH 6.0. ACR of the coated kobbah with TGase-treated GPF in the presence nanoparticles (MSN or CH–NPs) was reduced by 41.0% and 47.5%, respectively. However, the PEC containing CH–NPs showed the higher reduction of the ACR by 78.0%. Water content was higher in kobbah coated by PEC + CH–NPs solutions, while the oil content was lower. The color analysis indicated that kobbah with lower browning index containing lower ACR. Finally, in vitro digestion studies of both coating solutions and coated kobbah, demonstrated that the coating solutions and kobbah made by means of TGase or nanoparticles were efficiently digested.

A self-calibrating electrochemical aptasensing platform: Correcting external interference errors for the reliable and stable detection of avian influenza viruses

Conventional electrochemical biosensing systems rely on a single output signal, which limits their certain practical application, specifically from the viewpoint of external interference factors causing electrochemical signal errors. This study reports a self-calibrating dual-electrode based electrochemical aptasensor for the reliable and independent detection of avian influenza viruses (AIVs), which are the primary cause of highly contagious respiratory diseases, under external interference factors. Both electrodes were fabricated using tungsten rods surface-modified with a 3D nanostructured porous silica film (3DNRE). Subsequently, methylene blue (MB) was loaded as a redox-active material into the pores and capped with corresponding aptamer. One electrode was capped with an anti-AIV nucleoprotein (NP) aptamer (Apt_AIV-MB@3DNRE) allowing target-specific binding, resulting in changes in electrochemical signal upon diffusional release of the loaded redox molecules. The other electrode was capped with a control aptamer (Apt_con-MB@3DNRE), serving as a reference to correct false responses generated by nonspecific aptamer detachment and MB release under environmental changes in pH and ion strength and presence of nontarget molecules from cell lysis debris. In the dual-electrode platform, Apt_con-MB@3DNRE provides a corrected baseline for the fluctuating original output signals from Apt_AIV-MB@3DNRE. Consequently, this dual-electrode platform exhibits excellent output-signal stability (relative standard deviation, RSD: 5.86%) compared to a conventional single-electrode platform (RSD: 30.13%) at equivalent concentrations of AIV NP samples under different reaction buffer conditions. Moreover, no further purification and washing steps were required, indicating that the strategy may represent a universal and reliable platform for the electrochemical aptamer-based detection of various biomolecules.

Effect of Mesoporous Silica Nanoparticles on The Physicochemical Properties of Pectin Packaging Material for Strawberry Wrapping

Citrus peel pectin was used to prepare films (cast with or without glycerol) containing mesoporous silica nanoparticles. Nanoparticles reduced significantly the particle size, and had no effect on the Zeta potential of pectin solutions. Mechanical characterization demonstrates that pectin+nanoparticles containing films slightly increased tensile strength and significantly decreased the Young's modulus in comparison to films made only of pectin. However, elongation at the break increased in the pectin+nanoparticles films cast in the presence of glycerol, while both Young's modulus and tensile strength were reduced. Moreover, nanoparticles were able to reduce the barrier properties of pectin films prepared with or without glycerol, whereas positively affected the thermal stability of pectin films and the seal strength. The 0.6% pectin films reinforced or not with 3% nanoparticles in the presence of 30% glycerol were used to wrap strawberries in order to extend the fruit's shelf-life, over a period of eighty days, by improving their physicochemical properties.

Highly ordered 3D electrochemical DNA biosensor based on dual orientation controlled rolling motor and graftable tetrahedron DNA

Herein, a robust and highly ordered three-dimensional electrochemical DNA (3D E-DNA) biosensor was proposed, and its orientation was controlled from top down by poly adenine oligonucleotides (polyA-ODNs)-mediated rolling motor (PRM) and graftable tetrahedron DNA (GTD). The GTD with a grafting domain was immobilized on the electrode surface to construct a well-organized sensing interface and controlled the orientation and distribution of the whole system at the "bottom" of this biosensor. The polyA-ODNs regulated the direction and density of the leg DNA attached on PRM at the "top" of the biosensor. The motion was achieved through the target induced cyclic cleaving, which triggered the motor rolling rather than walk. Impressively, the duplex strand DNA (dsDNA) formed after grafting, as a girder, provided a stable support to the soft long single strand (ssDNA), which facilitated the formation of the catalytic center, elevated the efficiency of the rolling cleavage. Under the optimal conditions, the designed biosensor exhibited a lower limit of 0.17 nM and wide linear range from 0.5 nM to 1.5 μM for adenosine rapid detection. Unique dual orientation regulated characteristics of the system increased the probability hybridization enormously and improved the motion efficiency significantly, which offered new avenue of DNA nanomachines development in biosensor platform.

Instrument-free quantitative gold nanoparticle-based liquid-phase colorimetric assays for use in resource-poor environments

This work describes a new class of gold nanoparticle-based liquid-phase colorimetric assay (GNP-LPCA) termed as two dimensional (2D) GNP-LPCA that enables quantitative detection of model analytes with naked eye.