Cysteine-mediated aggregation of Au nanoparticles: the development of a H2O2 sensor and oxidase-based biosensors

Application of pyrite and chalcopyrite as sensor electrode for amperometric detection and measurement of hydrogen peroxide

The sensing performance of solid-state amperometric sensors based on natural sulfide minerals, i.e., pyrite and chalcopyrite, has been characterized for the detection and measurement of hydrogen peroxide (H₂O₂) in aqueous medium.

Unraveling the molecular mechanism of photosynthetic toxicity of highly fluorescent silver nanoclusters to Scenedesmus obliquus

While the discovery of numerous attractive properties of silver at the nanoscale has increased their demand in many sectors including medicine, optics, sensing, painting and cosmetics, it has also raised wide public concerns about their effect on living organisms in aquatic environment. Despite the continuous effort to understand the various aspects of the toxicity of silver nanomaterials, the molecular level understanding on their cytotoxicity mechanism to biological organisms has remained unclear. Herein, we demonstrated the underlying mechanism of the photosynthetic toxicity against green algae namely, Scenedesmus obliquus by using an emerging silver nanomaterial, called silver nanoclusters (defined as r-Ag NCs). By exploiting the unique fluorescence properties of r-Ag NCs along with various other analytical/biological tools, we proposed that the photosynthetic toxicity of r-Ag NCs was largely attributed to the "joint-toxicity" effect of particulate form of r-Ag NCs and its released Ag+, which resulted in the disruption of the electron transport chain of light reaction and affected the content of key enzymes (RuBP carboxylase/ oxygenase) of Calvin cycle of algae cells. We believe that the present study can also be applied to the assessment of the ecological risk derived from other metal nanoparticles.

Transformation of CuO Nanoparticles in the Aquatic Environment: Influence of pH, Electrolytes and Natural Organic Matter

Many studies have shown the effect of solution chemistry on the environmental behavior of metal-based nanoparticles (NPs), except CuO NPs. Here, we investigated the agglomeration, sedimentation, dissolution, and speciation of CuO NPs by varying pH, ionic strength, ionic valence, and natural organic matter (NOM). The results showed that as the pH moved away from 6, the size of CuO agglomerates decreased, along with the enhanced NP suspension stabilization, due to the increase of electrostatic repulsive force. Increasing ionic strength and valence intensified the agglomeration and sedimentation of CuO NPs because of the compression of electrical double layers. The presence of humic acid and citric acid enhanced the dispersion and stabilization of CuO NP suspension, but l-cysteine showed a different impact. Decreasing pH, increasing ionic strength and all NOM improved the dissolution of CuO NPs, but the divalent electrolyte (CaCl₂) inhibited the Cu²⁺ release from CuO NPs compared to the monovalent electrolyte (NaCl). In addition, X-ray absorption near edge structure (XANES) analysis demonstrated that the presence of l-cysteine transformed more than 30% of CuO NPs to Cu(I)-cysteine by coordinating with thiol group. This study can give us an in-depth understanding on the environmental behavior and fate of CuO NPs in the aquatic environment.

Turn-on Luminescent Probe for Hydrogen Peroxide Sensing and Imaging in Living Cells based on an Iridium(III) Complex-Silver Nanoparticle Platform

A sensitive turn-on luminescent sensor for H2O2 based on the silver nanoparticle (AgNP)-mediated quenching of an luminescent Ir(III) complex (Ir-1) has been designed. In the absence of H2O2, the luminescence intensity of Ir-1 can be quenched by AgNPs via non-radiative energy transfer. However, H2O2 can oxidize AgNPs to soluble Ag+ cations, which restores the luminescence of Ir-1. The sensing platform displayed a sensitive response to H2O2 in the range of 0-17 μM, with a detection limit of 0.3 μM. Importantly, the probe was successfully applied to monitor intracellular H2O2 in living cells, and it also showed high selectivity for H2O2 over other interfering substances.

Ellipsometry of Colloidal Solutions: New Experimental Setup and Application to Metallic Colloids

An ellipsometric cell is developed to simultaneously determine the shape distribution, the volume fraction, and the complex refractive index of gold and silver colloids. Simulation reveals that this cell drastically improves the detection limit of ellipsometry. Indeed, Ag and Au nanoparticles (NPs) are detected at the ppmv level. We demonstrate that the NPs shape distribution can be estimated from ellipsometric measurements by analyzing them with a shape distributed effective medium theory (SDEMT). The obtained distributions from ellipsometry are in agreement with those deduced from transmission electron microcopy (TEM). Contrary to TEM, ellipsometry probes a large number of NPs estimated at about 10¹¹ NPs. Finally, we show that the complex refractive index of colloids as determined from ellipsometry is sensitive to the optical properties of the solvent and the plasmonic properties of NPs.

Plasmon-Based Colorimetric Nanosensors for Ultrasensitive Molecular Diagnostics

Colorimetric detection of target analytes with high specificity and sensitivity is of fundamental importance to clinical and personalized point-of-care diagnostics. Because of their extraordinary optical properties, plasmonic nanomaterials have been introduced into colorimetric sensing systems, which provide significantly improved sensitivity in various biosensing applications. Here we review the recent progress on these plasmonic nanoparticles-based colorimetric nanosensors for ultrasensitive molecular diagnostics. According to their different colorimetric signal generation mechanisms, these plasmonic nanosensors are classified into two categories: (1) interparticle distance-dependent colorimetric assay based on target-induced forming cross-linking assembly/aggregate of plasmonic nanoparticles; and (2) size/morphology-dependent colorimetric assay by target-controlled growth/etching of the plasmonic nanoparticles. The sensing fundamentals and cutting-edge applications will be provided for each of them, particularly focusing on signal generation and/or amplification mechanisms that realize ultrasensitive molecular detection. Finally, we also discuss the challenge and give our future perspective in this emerging field.

Detection of Ca2+-induced acetylcholine released from leukemic T-cells using an amperometric microfluidic sensor

A microfluidic structured-dual electrodes sensor comprising of a pair of screen printed carbon electrodes was fabricated to detect acetylcholine, where one of them was used for an enzyme reaction and another for a detection electrode. The former was coated with gold nanoparticles and the latter with a porous gold layer, followed by electropolymerization of 2, 2:5,2-terthiophene-3-(p-benzoic acid) (pTTBA) on both the electrodes. Then, acetylcholinesterase was covalently attached onto the reaction electrode, and hydrazine and choline oxidase were co-immobilized on the detection electrode. The layers of both modified electrodes were characterized employing voltammetry, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and quartz crystal microscopy. After the modifications of both electrode surfaces, they were precisely faced each other to form a microfluidic channel structure, where H₂O₂ produced from the sequential enzymatic reactions was reduced by hydrazine to obtain the analytical signal which was analyzed by the detection electrode. The microfluidic sensor at the optimized experimental conditions exhibited a wide dynamic range from 0.7nM to 1500μM with the detection limit of 0.6 ± 0.1nM based on 3s (S/N = 3). The biomedical application of the proposed sensor was evaluated by detecting acetylcholine in human plasma samples. Moreover, the Ca²⁺-induced acetylcholine released in leukemic T-cells was also investigated to show the in vitro detection ability of the designed microfluidic sensor. Interference due to the real component matrix were also studied and long term stability of the designed sensor was evaluated. The analytical performance of the designed sensor was also compared with commercially available ACh detection kit.

Synthesis of Recombinant Mouse Crystallin Proteins and in Vitro Measurement of Their Refractivity

The eye lens is an organ that focuses light onto the retina and is reported to have a high refractive index in vertebrates. An analysis of refractivity was conducted using recombinant mouse Crystallin proteins produced in Escherichia coli (E. coli) compared with bovine serum albumin (BSA) and other commercially available proteins. Not only did we measure the refractivity but for one of the crystallins, Cryba1, we also confirmed that it responds uniquely to its environmental conditions. The crystallin showed high refractivity, as expected, and we confirmed that the electrical charge of the Cryba1 molecule influences its refractivity.

pH-Guided Self-Assembly of Copper Nanoclusters with Aggregation-Induced Emission

We here report a facile pH-guided strategy for the fabrication of water-soluble protein/copper nanoclusters (CuNCs) hybrid nanostructures with stable and bright luminescence resulted from aggregation-induced emission. Using l-cysteine as both the reducing and capping agents, the synthesized CuNCs showed a good reversible pH-responsive aggregation and dispersion in the solution. The CuNCs formed insoluble macroscopic aggregates with stable red-colored emission (620 nm) at pH 3.0 but became soluble with weak luminescence at pH <1.5 or pH >4.0. The highly reversible pH-responsive properties of the CuNCs made it feasible to achieve water-soluble protein/CuNCs hybrid nanostructures in the presence of protein without any external forces (e.g., sonication). The weak luminescent CuNCs were first mixed with protein under neutral condition (e.g., pH 7.0), followed by tuning of the pH to acidic conditions (e.g., pH 3.0) to form luminescent protein/CuNCs hybrid nanostructures, the sizes of which were much smaller than those of the protein-free macroscopic CuNC aggregates. This strategy was easily applicable to other dispersing agents (e.g., glucose oxidase), opening a new pathway for the construction of many other smart water-soluble luminescent biomolecule/nanocluster hybrid nanostructures with various applications.

Cu2+-catalyzed and H2O2-facilitated oxidation strategy for sensing copper(ii) based on cysteine-mediated aggregation of gold nanoparticles

A novel colorimetric Cu²⁺ sensor using polyethyleneglycol-stabilized gold nanoparticles has been developed based on a cysteine/H₂O₂ system.

Magnetic Iron Oxide Nanoparticle Seeded Growth of Nucleotide Coordinated Polymers

The introduction of functional molecules to the surface of magnetic iron oxide nanoparticles (NPs) is of critical importance. Most previously reported methods were focused on surface ligand attachment either by physisorption or covalent conjugation, resulting in limited ligand loading capacity. In this work, we report the seeded growth of a nucleotide coordinated polymer shell, which can be considered as a special form of adsorption by forming a complete shell. Among all of the tested metal ions, Fe(3+) is the most efficient for this seeded growth. A diverse range of guest molecules, including small organic dyes, proteins, DNA, and gold NPs, can be encapsulated in the shell. All of these molecules were loaded at a much higher capacity compared to that on the naked iron oxide NP core, confirming the advantage of the coordination polymer (CP) shell. In addition, the CP shell provides better guest protein stability compared to that of simple physisorption while retaining guest activity as confirmed by the entrapped glucose oxidase assay. Use of this system as a peroxidase nanozyme and glucose biosensor was demonstrated, detecting glucose as low as 1.4 μM with excellent stability. This work describes a new way to functionalize inorganic materials with a biocompatible shell.

Simple and Sensitive Colorimetric Detection of Dopamine Based on Assembly of Cyclodextrin-Modified Au Nanoparticles

A controlled assembly of natural beta-cyclodextrin modified Au NPs mediated by dopamine is demonstrated. Furthermore, a simple and sensitive colorimetric detection for dopamine is established by the concentration-dependent assembly.

1,4-Benzenediboronic-Acid-Induced Aggregation of Gold Nanoparticles: Application to Hydrogen Peroxide Detection and Biotin-Avidin-Mediated Immunoassay with Naked-Eye Detection

Hydrogen-peroxide (H2O2)-induced growth of small-sized gold nanoparticles (AuNPs) is often implemented for H2O2 sensing and plasmonic immunoassay. In contrast, there is little-to-no information in the literature regarding the application of H2O2-inhibited aggregation of citrate-capped AuNPs. This study discloses that benzene-1,4-diboronic acid (BDBA) was effective in driving the aggregation of citrate-capped AuNPs through an interaction between α-hydroxycarboxylate of citrate and boronic acids of BDBA. The H2O2-mediated oxidation of BDBA resulted in the conversion of boronic acid groups to phenol groups. The oxidized BDBA was incapable of triggering the aggregation of citrate-capped AuNPs. Thus, the presence of H2O2 prohibited BDBA-induced aggregation of citrate-capped AuNPs. The BDBA-induced aggregation of citrate-capped AuNPs can be paired with the glucose oxidase (GOx)-glucose system to design a colorimetric probe for glucose. Moreover, a H2O2·BDBA·AuNP probe was integrated with sandwich immunoassay, biotinylated antibody, and avidin-conjugated GOx for the selective naked-eye detection of rabbit immunoglobulin G (IgG) and human-prostate-specific antigen (PSA). The lowest detectable concentrations of rabbit IgG and human PSA by the naked eye were down to 0.1 and 4 ng/mL, respectively. More importantly, the proposed plasmonic immunoassay allowed the naked-eye quantification of 0-10 ng/mL PSA at an interval of 2 ng/mL in plasma samples.

Highly Catalytic Nanodots with Renal Clearance for Radiation Protection

Ionizing radiation (gamma and X-ray) is widely used in industry and medicine, but it can also pose a significant hazardous effect on health and induce cancer, physical deformity, and even death, due to DNA damage and invasion of free radicals. There is therefore an urgent unmet demand in designing highly efficient radioprotectants with synergetic integration of effective renal clearance and low toxicity. In this study, we designed ultrasmall (sub-5 nm) highly catalytically active and cysteine-protected MoS2 dots as radioprotectants and investigated their application in protection against ionizing radiation. In vivo preclinical studies showed that the surviving fraction of MoS2-treated mice can appreciably increase to up to 79% when they were exposed to high-energy ionizing radiation. Furthermore, MoS2 dots can contribute in cleaning up the accumulated free radicals within the body, repairing DNA damage, and recovering all vital chemical and biochemical indicators, suggesting their unique role as free radical scavengers. MoS2 dots showed rapid and efficient urinary excretion with more than 80% injected dose eliminated from the body after 24 h due to their ultrasmall hydrodynamic size and did not cause any noticeable toxic responses up to 30 days.

Gold Aerogels: Three-Dimensional Assembly of Nanoparticles and Their Use as Electrocatalytic Interfaces

Three-dimensional (3D) porous metal nanostructures have been a long sought-after class of materials due to their collective properties and widespread applications. In this study, we report on a facile and versatile strategy for the formation of Au hydrogel networks involving the dopamine-induced 3D assembly of Au nanoparticles. Following supercritical drying, the resulting Au aerogels exhibit high surface areas and porosity. They are all composed of porous nanowire networks reflecting in their diameters those of the original particles (5-6 nm) via electron microscopy. Furthermore, electrocatalytic tests were carried out in the oxidation of some small molecules with Au aerogels tailored by different functional groups. The beta-cyclodextrin-modified Au aerogel, with a host-guest effect, represents a unique class of porous metal materials of considerable interest and promising applications for electrocatalysis.

Synthesis of porous NiO/CeO2 hybrid nanoflake arrays as a platform for electrochemical biosensing

Porous NiO/CeO2 hybrid nanoflake arrays fabricated by a facile hydrothermal method were employed as substrates for electrochemical biosensors. The resulting NiO/CeO2 hybrid nanoflake arrays with a large specific surface area and good biocompatibility presented an excellent platform for electrochemical biosensing.

Fast preparation of MoS2 nanoflowers decorated with platinum nanoparticles for electrochemical detection of hydrogen peroxide

MoS₂ nanoflowers decorated with Pt nanoparticles show enhanced performances for electrochemical H₂O₂ sensing.

Prussian blue nanoparticles encapsulated inside a metal–organic framework via in situ growth as promising peroxidase mimetics for enzyme inhibitor screening

Metal–organic framework-based peroxidase mimetics for enzyme-inhibitor screening.

Gold nanoparticles as sensitive optical probes

Recent advances in Au NP based optical sensing systems for various analytes based on absorption, fluorescence and SERS are summarized.

Ultrasensitive electrospun fluorescent nanofibrous membrane for rapid visual colorimetric detection of H2O2

We report herein a flexible fluorescent nanofibrous membrane (FNFM) prepared by decorating the gold nanocluster (AuNC) on electrospun polysulfone nanofibrous membrane for rapid visual colorimetric detection of H2O2. The provision of AuNC coupled to NFM has proven to be advantageous for facile and quick visualization of the obtained results, permitting instant, selective, and on-site detection. We strongly suggest that the fast response time is ascribed to the enhanced probabilities of interaction with AuNC located at the surface of NF. It has been observed that the color change from red to blue is dependent on the concentration, which is exclusively selective for hydrogen peroxide. The detection limit has been found to be 500 nM using confocal laser scanning microscope (CLSM), visually recognizable with good accuracy and stability. A systematic comparison was performed between the sensing performance of FNFM and AuNC solution. The underlying sensing mechanism is demonstrated using UV spectra, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The corresponding disappearance of the characteristic emissions of gold nanoclusters and the emergence of a localized surface plasmon resonance (LSPR) band, stressing this unique characteristic of gold nanoparticles. Hence, it is evident that the conversion of nanoparticles from nanoclusters has taken place in the presence of H2O2. Our work here has paved a new path for the detection of bioanalytes, highlighting the merits of rapid readout, sensitivity, and user-friendliness.

A RET-supported logic gate combinatorial library to enable modeling and implementation of intelligent logic functions

A logic gate combinatorial library, including basic logic gates, a single three-input NOR gate, and combinatorial gates to realize intelligent logic functions (keypad-lock, parity checker) is constructed.

Boolean logic gates integrate multiple digital inputs into a digital output. Among these, logic gates based on nucleic acids have attracted a great deal of attention due to the prospect of controlling living systems in the way we control electronic computers. Herein, by employing Thioflavin T (ThT) as a signal transducer, we integrated multiple components based on RET (a type of proto-oncogene) into a logic gate combinatorial library, including basic logic gates (NOR, INHIBIT, IMPLICATION), a single three-input NOR gate, and combinatorial gates (INHIBIT–OR, NOT–AND–NOR). In this library, gates were connected in series where the output of the previous gate was the input for the next gate. Subsequently, by taking advantage of the library, some intelligent logic functions were realized. Expectedly, a biocomputing keypad-lock security system was designed by sequential logic operations. Moreover, a parity checker which can identify even numbers and odd numbers from natural numbers was established successfully. This work helps elucidate the design rules by which simple logic can be harnessed to produce diverse and complex calculations by rewiring communication between different gates. Together, our system may serve as a promising proof of principle that demonstrates increased computational complexity by linking multiple logic gates together.

Soft landing of bare PtRu nanoparticles for electrochemical reduction of oxygen

Magnetron sputtering of two independent Pt and Ru targets coupled with inert gas aggregation in a modified commercial source has been combined with soft landing of mass-selected ions to prepare bare 4.5 nm diameter PtRu nanoparticles on glassy carbon electrodes with controlled size and morphology for electrochemical reduction of oxygen in solution. Employing atomic force microscopy (AFM) it is shown that the nanoparticles bind randomly to the glassy carbon electrode at a relatively low coverage of 7 × 10(4) ions μm(-2) and that their average height is centered at 4.5 nm. Scanning transmission electron microscopy images obtained in the high-angle annular dark field mode (HAADF-STEM) further confirm that the soft-landed PtRu nanoparticles are uniform in size. Wide-area scans of the electrodes using X-ray photoelectron spectroscopy (XPS) reveal the presence of both Pt and Ru in atomic concentrations of ∼9% and ∼33%, respectively. Deconvolution of the high energy resolution XPS spectra in the Pt 4f and Ru 3d regions indicates the presence of both oxidized Pt and Ru. The substantially higher loading of Ru compared to Pt and enrichment of Pt at the surface of the nanoparticles is confirmed by wide-area analysis of the electrodes using time-of-flight medium energy ion scattering (TOF-MEIS) employing both 80 keV He(+) and O(+) ions. The activity of electrodes containing 7 × 10(4) ions μm(-2) of bare 4.5 nm PtRu nanoparticles toward the electrochemical reduction of oxygen was evaluated employing cyclic voltammetry (CV) in 0.1 M HClO4 and 0.5 M H2SO4 solutions. In both electrolytes a pronounced reduction peak was observed during O2 purging of the solution that was not evident during purging with Ar. Repeated electrochemical cycling of the electrodes revealed little evolution in the shape or position of the voltammograms indicating high stability of the nanoparticles supported on glassy carbon. The reproducibility of the nanoparticle synthesis and deposition was evaluated by employing the same experimental parameters to prepare nanoparticles on glassy carbon electrodes on three occasions separated by several days. Surfaces with almost identical electrochemical behavior were observed with CV, demonstrating the highly reproducible preparation of bare nanoparticles using physical synthesis in the gas-phase combined with soft landing of mass-selected ions.

Enzymatic reaction modulated gold nanorod end-to-end self-assembly for ultrahigh sensitively colorimetric sensing of cholinesterase and organophosphate pesticides in human blood

We present herein the first reported self-assembly modulation of gold nanorods (AuNRs) by enzymatic reaction, which is further employed for colorimetric assays of cholinesterase (ChE) and organophosphate pesticides (OPs) in human blood. ChE catalyzes its substrate (acetylthiocholine) and produces thiocholine and acetate acid. The resulting thiols then react with the tips of the AuNRs by S-Au conjunction and prevent subsequent cysteine-induced AuNR end-to-end (EE) self-assembly. Correspondingly, the AuNR surface plasmon resonance is regulated, which results in a distinctly ratiometric signal output. Under optimal conditions, the linear range is 0.042 to 8.4 μU/mL, and the detection limit is as low as 0.018 μU/mL. As ChE is incubated with OPs, the enzymatic activity is inhibited. So, the cysteine-induced assembly is observed again. On the basis of this principle, OPs can be well determined ranging from 0.12 to 40 pM with a 0.039 pM detection limit. To our knowledge, the present quasi pU/mL level sensitivity for ChE and the quasi femtomolar level sensitivity for OPs are at least 500 and 7000 times lower than those of previous colorimetric methods, respectively. The ultrahigh sensitivity results from (1) the rational choice of anisotropic AuNRs as building blocks and reporters and (2) the specific structure of the enzymatic thiocholine. Because of ultrahigh sensitivity, serum samples are allowed to be extremely diluted in the assay. Accordingly, various nonspecific interactions, even from glutathione/cysteine, are well avoided. So, both ChE and OPs in human blood can be directly assayed without any prepurification, indicating the simplicity and practical promise of the proposed method.

Poly(thymine)-Templated Copper Nanoparticles as a Fluorescent Indicator for Hydrogen Peroxide and Oxidase-Based Biosensing

Biomineralized fluorescent metal nanoparticles have attracted considerable interest in many fields by virtue of their excellent properties in synthesis and application. Poly(thymine)-templated fluorescent copper nanoparticles (T-CuNPs) as a promising nanomaterial has been exploited by us recently and displays great potential for signal transducing in biochemical analysis. However, the application of T-CuNPs is rare and still at an early stage. Here, a new fluorescent analytical strategy has been developed for H2O2 and oxidase-based biosensing by exploiting T-CuNPs as an effective signal indicator. The mechanism is mainly based on the poly(thymine) length-dependent formation of T-CuNPs and the probe's oxidative cleavage. In this assay, the probe T40 can effectively template the formation of T-CuNPs by a fast in situ manner in the absence of H2O2, with high fluorescent signal, while the probe is cleaved into short-oligonucleotide fragments by hydroxyl radical (·OH) which is formed from the Fenton reaction in the presence of H2O2, leading to the decline of fluorescence intensity. By taking advantage of H2O2 as a mediator, this strategy is further exploited for oxidase-based biosensing. As the proof-of-concept, glucose in human serum has been chosen as the model system and has been detected, and its practical applicability has been investigated by assay of real clinical blood samples. Results demonstrate that the proposed strategy has not only good detection capability but also eminent detection performance, such as simplicity and low-cost, holding great potential for constructing effective sensors for biochemical and clinical applications.

Time-resolved probes and oxidase-based biosensors using terbium(III)-guanosine monophosphate-mercury(II) coordination polymer nanoparticles

A novel lanthanide coordination polymer nanoparticle (LCPN)-based ternary complex was synthesized via the self-assembly of a terbium ion (Tb(3+)) with a nucleotide (GMP) and a mercury ion (Hg(2+)) in aqueous solution. The as-prepared LCPN-based ternary complex (Tb-GMP-Hg) can be applied to the development of time-resolved luminescence assays and oxidase-based biosensors.

Reversible catalysis for the reaction between methyl orange and NaBH4 by silver nanoparticles

The reaction between MO and NaBH4 catalyzed by Ag NPs has been studied. Ag NPs catalyzed the reduction of MO rapidly, while adding CTAB into the solution caused the regeneration of MO. Thus, reversible catalysis for the reaction between MO and NaBH4 by Ag NPs was discovered for the first time.

Dynamic biointerfaces: from recognition to function

The transformation of recognition signals into regulating macroscopic behaviors of biological entities (e.g., biomolecules and cells) is an extraordinarily challenging task in engineering interfacial properties of artificial materials. Recently, there has been extensive research for dynamic biointerfaces driven by biomimetic techniques. Weak interactions and chirality are two crucial routes that nature uses to achieve its functions, including protein folding, the DNA double helix, phospholipid membranes, photosystems, and shell and tooth growths. Learning from nature inspires us to design dynamic biointerfaces, which usually take advantage of highly selective weak interactions (e.g., synergetic chiral H-bonding interactions) to tailor their molecular assemblies on external stimuli. Biomolecules can induce the conformational transitions of dynamic biointerfaces, then drive a switching of surface characteristics (topographic structure, wettability, etc.), and eventually achieve macroscopic functions. The emerging progresses of dynamic biointerfaces are reviewed and its role from molecular recognitions to biological functions highlighted. Finally, a discussion is presented of the integration of dynamic biointerfaces with the basic biochemical processes, possibly solving the big challenges in life science.

Soft landing of bare nanoparticles with controlled size, composition, and morphology

Physical synthesis employing magnetron sputtering and gas aggregation in a modified commercial source has been coupled with size-selection and ion soft landing to prepare bare nanoparticles on surfaces with controlled coverage, size, composition, and morphology. Employing atomic force microscopy (AFM) and scanning electron microscopy (SEM), it is demonstrated that the size and coverage of nanoparticles on flat and stepped surfaces may be controlled using a quadrupole mass filter and the length of deposition, respectively. AFM shows that nanoparticles bind randomly to flat surfaces when soft landed at relatively low coverage (4 × 10(4) ions μm(-2)). On stepped surfaces at intermediate coverage (4 × 10(5) ions μm(-2)) nanoparticles bind along step edges forming extended linear chains. At the highest coverage (2 × 10(6) ions μm(-2)) nanoparticles form a continuous film on flat surfaces. On one surface with sizable defects, the presence of localized imperfections results in agglomeration of nanoparticles onto these features and formation of neighboring zones devoid of particles. Employing high resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) the customized magnetron sputtering/gas aggregation source is demonstrated to produce bare single metal particles with controlled morphology as well as bimetallic alloy nanoparticles with defined core-shell structures of that are of interest to catalysis.

Silver nanoprism etching-based plasmonic ELISA for the high sensitive detection of prostate-specific antigen

Ultrasensitive and quantitative detection using simple and low-cost assays is critical in clinical diagnostics. In this report, we developed a triangular silver nanoprism (AgNPRs) etching-based plasmonic biosensor for the detection of cancer biomarkers. The triangular AgNPRs-based plasmonic biosensor is an enzyme-linked immunosorbent assay combined with the enzyme-mediated surface plasmon resonance (SPR) of triangular AgNPRs. Triangular AgNPRs uses the immune response of prostate-specific antigen (PSA) to trigger the glucose oxidase (GOx)-catalysed oxidation of glucose (Glu), producing hydrogen peroxide. Hydrogen peroxide acts as an oxidant to etch the triangular AgNPRs into smaller spherical silver nanoparticles, which is accompanied by a substantial blueshift of the SPR peak and a colourimetric blue-to-purple change that can be observed by the naked eye. The SPR peak shift enables the quantitative assessment of PSA due to the remarkable colour change. The triangular AgNPRs-based plasmonic ELISA approach exhibited a quasilinear response to logarithmic PSA concentrations in the range of 10fg/mL to 100pg/mL with a limit of detection (LOD) of 4.1fg/mL. In addition, the LOD of PSA in this approach exceeds that of the conventional HRP-based ELISA (1.25ng/mL) approach by more than 5 orders of magnitude. Patient serum samples from 16 donors were assayed with triangular AgNPRs-based plasmonic ELISA. The results from the triangular AgNPRs-based immunoassay and the time-resolved fluorescence immunoassay showed excellent correlation, and there were no significant differences in the quantified amounts of PSA. The triangular AgNPRs-based plasmonic ELISA approach has advantages (ultrasensitive, cost-effective, ease of operation) that are expected to be of great interest in diagnostics and to be suitable for a point-of-care test.

Sensitive colorimetric assays for α-glucosidase activity and inhibitor screening based on unmodified gold nanoparticles

A colorimetric sensor has been developed in this work to sensitively detect α-glucosidase activity and screen α-glucosidase inhibitors (AGIs) utilizing unmodified gold nanoparticles (AuNPs). The sensing strategy is based on triple-catalytic reaction triggered by α-glucosidase. In the presence of α-glucosidase, aggregation of AuNPs is prohibited due to the oxidation of cysteine to cystine in the system. However, with addition of AGIs, cysteine induced aggregation of AuNPs occurs. Thus, a new method for α-glucosidase activity detection and AGIs screening is developed by measuring the UV-vis absorption or visually distinguishing. A well linear relation is presented in a range of 0.0025-0.05 U mL(-1). The detection limit is found to be 0.001 U mL(-1) for α-glucosidase assay, which is one order of magnitude lower than other reports. The IC50 values of four kinds of inhibitors observed with this method are in accordance with other reports. The using of unmodified AuNPs in this work avoids the complicated and time-consuming modification procedure. This simple and efficient colorimetric method can also be extended to other enzymes assays.