Silver nanoislands on cellulose fibers for chromatographic separation and ultrasensitive detection of small molecules

Solid-State Dewetting of Thin Au Films for Surface Functionalization of Biomedical Implants

Biomaterial-centered infections of orthopedic implants remain a significant burden in the healthcare system due to sedentary lifestyles and an aging population. One approach to combat infections and improve implant osteointegration is functionalizing the implant surface with anti-infective and osteoinductive agents. In this framework, Au nanoparticles are produced on the surface of Ti-6Al-4V medical alloy by solid-state dewetting of 5 nm Au film and used as the substrate for the conjugation of a model antibiotic vancomycin via a mono-thiolated poly(ethylene glycol) linker. Produced Au nanoparticles on Ti-6Al-4V surface are equiaxed with a mean diameter 19.8 ± 7.2 nm, which is shown by high-resolution scanning electron microscopy and atomic force microscopy. The conjugation of the antibiotic vancomycin, 18.8 ± 1.3 nm-thick film, is confirmed by high resolution-scanning transmission electron microscopy and X-ray photoelectron spectroscopy. Overall, showing a link between the solid-state dewetting process and surface functionalization, we demonstrate a novel, simple, and versatile method for functionalization of implant surfaces.

Facile and Low-Cost Fabrication of SiO2-Covered Au Nanoislands for Combined Plasmonic Enhanced Fluorescence Microscopy and SERS

An easy and low-cost way to fabricate monometallic Au nanoislands for plasmonic enhanced spectroscopy is presented. The method is based on direct thermal evaporation of Au on glass substrates to form nanoislands, with thicknesses between 2 and 15 nm, which are subsequently covered by a thin layer of silicon dioxide. We have used HR-SEM and AFM to characterize the nanoislands, and their optical transmission reveals strong plasmon resonances in the visible. The plasmonic performance of the fabricated substrates has been tested in fluorescence and Raman scattering measurements of two probe materials. Enhancement factors up to 1.8 and 9×104 are reported for confocal fluorescence and Raman microscopies, respectively, which are comparable to others obtained by more elaborated fabrication procedures.

Homogenous high enhancement surface-enhanced Raman scattering (SERS) substrates by simple hierarchical tuning of gold nanofoams

Surface enhanced Raman scattering (SERS) is a powerful tool for vibrational spectroscopy, providing orders of magnitude increase in chemical sensitivity compared to spontaneous Raman scattering. Yet it remains a challenge to synthesize robust, uniform SERS substrates quickly and easily. Lithographic approaches to produce substrates can achieve high, uniform sensitivity but are expensive and complex, thus difficult to scale. Facile solution-phase chemical approaches often result in unreliable SERS substrates due to heterogeneous arrangement of "hot spots" throughout the material. Here we demonstrate the synthesis and characterization of a homogeneous gold nanofoam (AuNF) substrate produced by a rapid, one-pot, four-ingredient synthetic approach. AuNFs are rapidly nucleated with macroscale porosity and then chemically roughened to produce nanoscale features that confer homogeneous and high signal enhancement (~10⁹) across large areas, a comparable performance to lithographically produced substrates.

Detection of aflatoxin B1 with a new label-free fluorescence aptasensor based on PVP-coated single-walled carbon nanohorns and SYBR Gold

This paper describes a novel fluorescence label-free aptasensor to detect aflatoxin B₁ (AFB₁) by utilizing SYBR Gold, aptamer, and single-walled carbon nanohorns (SWCNHs). In the presence of AFB₁, the conformation of AFB₁-specific aptamer went through and the spatial structure of this specific aptamer was transformed accordingly. Due to the resistance of the transformed aptamer when adsorbed on the surface of SWCNHs, the protection of the fluorescence of SYBR Gold was accomplished. Consequently, concentrations of AFB₁ showed a strong association with fluorescence intensity. The detection limit (LOD) of AFB₁ was 1.89 ng/mL, while the linear range was 5-200 ng/mL and fluorescence intensity satisfactorily correlated (R² = 0.9919) with the logarithm of AFB₁ concentration.

On-chip Paper Electrophoresis for Ultrafast Screening of Infectious Diseases

The outbreak of new viral strains promotes advances in universal diagnostic techniques for detecting infectious diseases with unknown viral sequence. Long double-stranded RNA (dsRNA), a hallmark of infections, serves as a virus marker for prompt detection of viruses with unknown genomes. Here, we report on-chip paper electrophoresis for ultrafast screening of infectious diseases. Negatively charged RNAs pass through the micro and nanoscale pores of cellulose in order of size under an external electric field applied to the paper microfluidic channel. Quantitative separation of long dsRNA mimicking poly I:C was analyzed from 1.67 to 33 ng·μL−1, which is close to the viral dsRNA concentration in infected cells. This paper-based capillary electrophoresis chip (paper CE chip) can provide a new diagnostic platform for ultrafast viral disease detection at the point-of-care (POC) level.

High rotational speed hand-powered triboelectric nanogenerator toward a battery-free point-of-care detection system

The timely biochemical detection of environmental pollutants or infectious disease is a predominant challenge for global health and people living in remote areas. However, the energy supply is still difficult for both the pretreatment and test steps, especially for diagnostics in resource-limited environments or outdoor point-of-care testing. Herein, we demonstrate a hand-powered triboelectric nanogenerator (TENG) system, which can simultaneously accomplish centrifugal pretreatment and analysis without an additional power supply. The complete separation of plasma from red blood cells can be achieved within 1.5 min at an operation frequency of 1 Hz. Besides, according to the impressive high rotational speed of 7500 rpm, the rotating mechanical energy can be efficiently recycled by the TENG to power different electronic devices, such as an electronic watch or thermometer. As a demonstration, the pretreatment of lake water and the detection of hydrogen peroxide contained in it has been realized. The combination of the system with different types of sensors will further promote its applications in multifarious biochemical detections. Moreover, this TENG system is effective, field-portable and ultra-low cost, and is promising for battery-free point-of-care diagnostic systems for outdoor or harsh environments.

A hand-powered TENG system has been developed to kill two birds with one stone, simultaneously realizing centrifugation and rotary mechanical energy harvesting. Then, centrifugation of lake water and detection of H₂O₂ in it has been realized.

Paper-Based Multiplex Surface-Enhanced Raman Scattering Detection Using Polymerase Chain Reaction Probe Codification

We construct a multiplex surface-enhanced Raman scattering (SERS) platform based on a plasmonic paper substrate and a double-labeled probe for the detection of multiple fluorescent dyes at high sensitivity in a single-wavelength light source system. Plasmonic paper, made of silver nanodots on three-dimensional cellulose fibers, enables highly sensitive SERS biosensing based on localized surface plasmon resonance (LSPR). The proposed method enables the identification and quantification of a range of fluorescent dyes ranging from picomolar to millimolar concentrations. The use of 5' fluorescent dyes and 3' biotin-modified probes as SERS-coded probes renders possible the separation of fluorescent dyes with streptavidin-coated magnetic beads (SMBs) and the sensitive detection of multiple dyes after the reverse transcription polymerase chain reaction (RT-PCR). This experimental study reveals the multiplex detection capability of PCR-based SERS under existing PCR conditions without modifying primer and probe sequences. The combination of magnetic bead-based separation and paper SERS platform is efficient, economical, and can be used for the simultaneous detection of two or more pathogens.

An ATP responsive fluorescent supramolecular assembly based on a polyelectrolyte and an AIE active tetraphenylethylene derivative

Aggregation induced emission (AIE) active probes have attracted enormous attention due to their wide-spread and ever increasing number of applications in the sensing of chemically and biologically important molecules. AIE probes undergo drastic modulation in their photophysical features from a monomeric to aggregated state. In the current work, we report the aggregation of tetra-anionic Su-TPE (AIE active probe) in the presence of a cationic polyelectrolyte, poly(allylaminehydrochloride) (PAH). A supramolecular assembly is formed by the electrostatic interaction between cationic PAH and anionic Su-TPE molecules, which leads to drastic modulations in the spectral features of anionic Su-TPE upon addition of cationic PAH. The Su-TPE-PAH aggregate assembly has been investigated using various photophysical techniques, such as, ground-state absorption, steady-state and time-resolved emission spectroscopic techniques along with 1H NMR measurements. The Su-TPE-PAH aggregate assembly is found to be responsive towards the ionic strength of the medium and temperature which results in drastic modulations of the spectral features of the emissive supramolecular aggregate assembly. Finally, the specific recognition of an important bioanalyte, ATP, has been achieved using the formed Su-TPE-PAH supramolecular aggregate assembly as a sensing platform which displays good selectivity and high sensitivity towards ATP. Importantly, the developed sensor platform could also function in the human serum matrix, hence, demonstrating the potential of the established sensor platform for real-life applications in near future.

Detection of aflatoxin B1 with a new label-free fluorescent aptasensor based on exonuclease I and SYBR Gold

This paper describes a new label-free fluorescent aptasensor for the detection of aflatoxin B1 (AFB1) based upon exonuclease I (Exo I) and SYBR Gold, in which SYBR Gold, aptamer, AFB1, and Exo I were used. Specific combinations of aptamer and AFB1 occurred in the presence of AFB1 and consequently altered the spatial structure of the aptamer, thereby preventing its digestion by Exo I. When SYBR Gold was added, intense fluorescence was observed. Additionally, a good linear relationship was observed under optimized conditions between the fluorescence intensities and the AFB1 concentrations (R2 = 0.993). The established aptamer sensor was highly sensitive and exhibited a low limit of detection of 1.82 ng mL-1, with superior specificity for AFB1. It was also used in the quantification of AFB1 levels in soybean sauce samples and demonstrated satisfactory recoveries in the scope of 94.8-108.9%. The proposed sensor is highly sensitive, low cost, and capable of rapid detection and can thus be used to determine mycotoxin levels in a wide range of feeds and food products in a high-throughput and quantitative means.

Zinc oxide nanoparticles decorated fluorescent and antibacterial glass fiber pre-filter paper

Zinc oxide nanoparticles (ZnO–NPs) were synthesized and decorated simultaneously onto the glass fiber pre-filter paper (GF paper) by the sonochemical method without using any additional reagents (a ‘Green’ synthesis approach). ZnO–NPs decorated GF paper was characterized by electron, confocal laser scanning and atomic force microscopy, fourier transform infrared and atomic emission spectroscopy, X-ray diffraction, and thermogravimetric analysis etc. Due to the massive void volume space, exceptional dimensional stability, large thickness (790 μm) of the GF paper (unlike other paper materials) and ultrasonic irradiation effects, ZnO–NPs were decorated in the enormous amount (96 mg per paper) without causing any adverse effects on the GF paper. Such a huge amount decoration onto GF paper makes it multifunctional, fluorescencet (orange-pink color, 535–624 nm) under ultra-violet light (360 nm) and antibacterial. The antibacterial activity of the ZnO–NPs decorated GF paper was examined against Gram-positive bacteria Bacillus subtilis 168 and Staphylococcus aureus (MCC 2043, pathogenic). The outcomes from the antibacterial experiments revealed ∼99% (2 log) reduction in the survival of the filtered bacteria (B. subtilis) on the ZnO–NPs decorated GF paper due to the toxicity of ZnO–NPs on bacterial cells like cell shrinkage, cytoplasmic leakage, cell burst, etc. Multifunctional, ZnO–NPs decorated GF paper could be used for fluorescencet and antibacterial paper-based applications.

Self-assembled plasmonics for angle-independent structural color displays with actively addressed black states

Functional nanomaterials will enable the next generation of displays, detectors, and photovoltaic devices by interacting with light at subwavelength length scales. However, performance and practical integration with current electronic systems remain a scientific and engineering challenge. Here, we report the wafer-scale self-assembly/growth of nanoparticles which reproduce the cyan, magenta, and yellow color space. We explore the physics of the optical resonances and the advantageous properties they manifest for color filter technology, such as angle insensitivity and high saturation. The versatile formation process then enables integration with commercial devices to realize a hybrid, nanoparticle–liquid crystal reflective display.

Nanostructured plasmonic materials can lead to the extremely compact pixels and color filters needed for next-generation displays by interacting with light at fundamentally small length scales. However, previous demonstrations suffer from severe angle sensitivity, lack of saturated color, and absence of black/gray states and/or are impractical to integrate with actively addressed electronics. Here, we report a vivid self-assembled nanostructured system which overcomes these challenges via the multidimensional hybridization of plasmonic resonances. By exploiting the thin-film growth mechanisms of aluminum during ultrahigh vacuum physical vapor deposition, dense arrays of particles are created in near-field proximity to a mirror. The sub-10-nm gaps between adjacent particles and mirror lead to strong multidimensional coupling of localized plasmonic modes, resulting in a singular resonance with negligible angular dispersion and ∼98% absorption of incident light at a desired wavelength. The process is compatible with arbitrarily structured substrates and can produce wafer-scale, diffusive, angle-independent, and flexible plasmonic materials. We then demonstrate the unique capabilities of the strongly coupled plasmonic system via integration with an actively addressed reflective liquid crystal display with control over black states. The hybrid display is readily programmed to display images and video.

A label-free fluorometric aptasensor for adenosine triphosphate (ATP) detection based on aggregation-induced emission probe

Based on Aggregation-Induced Emission (AIE), the development of a label-free, simple and sensitive fluorometric aptasensor for adenosine triphosphate (ATP) detection is described. With ATP present, the aptamers will combine with ATP and the conformation of the aptamer will switch from a random coil to an antiparallel G-quadruplex, which impedes the digestion by exonuclease I (Exo I). Addition of 4,4 -(1E,1E)-2,2-(anthracene-9,10-diyl) bis (ethene-2,1-diyl) bis (N,N, N-trimethyl-benzenaminium iodide) (DSAI) into the solution will cause aggregation of DSAI on the surface of the aptamer/ATP complex and consequently give rise to strong emission. Additionally, a good linear relationship was observed under optimized conditions between the fluorescence intensities and the logarithm of ATP concentrations (R² = 0.9908). The established aptamer sensor was highly sensitive and exhibited a low limit of detection of 32.8 nM, with superior specificity for ATP. It was also used in the quantification of ATP levels in human serum samples and demonstrated satisfactory recoveries in the scope of 93.2%-107.6%. The cellular ATP assay results indicated that the developed method can be used for monitoring ATP concentrations in cell extracts without the interference of other substances in the cells. This method offers several advantages such as simplicity, rapidity, low cost and excellent selectivity, which make it hold great potential for the detection of ATP in bioanalytical and biological studies.

Nanoislands as plasmonic materials

Subwavelength metal nanoislands thermally dewetted from a thin film emerge as a powerful and cost-effective photonic material, due to the formation of substantially strong nano-gap-based plasmonic hot spots and their simple large-area nanofabrication. Unlike conventional nanostructures, nanoislands dewetted from thin metal films can be formed on a large scale at the wafer level and show substrate-dependent plasmonic phenomena across a broad spectral range from ultraviolet to infrared. Substrate-selective dewetting methods for metal nanoislands enable diverse nanophotonic and optoelectronic technologies, underlining mechanical, structural, and material properties of a substrate. Emerging bioplasmonic technology using metal nanoislands also serves as a high-throughput and surface-sensitive analytical technique with wide-ranging application in rapid, real-time, and point-of-care medical diagnostics. This review introduces an assortment of dewetting fabrication methods for metal nanoislands on distinct substrates from glass to cellulose fibers and provides novel findings for metal nanoislands on a substrate by three-dimensional numerical modeling. Furthermore, the plasmonic properties of metal nanoislands and recent examples for their photonic applications, in particular, biological sensing, are technically summarized and discussed.

Generalized On-Demand Production of Nanoparticle Monolayers on Arbitrary Solid Surfaces via Capillarity-Mediated Inverse Transfer

Century-old Langmuir monolayer deposition still represents the most convenient approach to the production of monolayers of colloidal nanoparticles on solid substrates for practical biological and chemical-sensing applications. However, this approach simply yields arbitrarily shaped large monolayers on a flat surface and is strongly limited by substrate topography and interfacial energy. Here, we describe a generalized and facile method of rapidly producing uniform monolayers of various colloidal nanoparticles on arbitrary solid substrates by using an ordinary capillary tube. Our method is based on an interesting finding of inversion phenomenon of a nanoparticle-laden air-water interface by flowing through a capillary tube in a manner that prevents the particles from adhesion to the capillary sidewall, thereby presenting the nanoparticles face-first at the tube's opposite end for direct and one-step deposition onto a substrate. We show that our method not only allows the placement of a nanoparticle monolayer at target locations of solid substrates regardless of their surface geometry and adhesion but also enables the production of monolayers containing nanoparticles with different size, shape, surface charge, and composition. To explore the potential of our approach, we demonstrate the facile integration of gold nanoparticle monolayers into microfluidic devices for the real-time monitoring of molecular Raman signals under dynamic flow conditions. Moreover, we successfully extend the use of our method to developing on-demand Raman sensors that can be built directly on the surface of consumer products for practical chemical sensing and fingerprinting. Specifically, we achieve both the pinpoint deposition of gold nanoparticle monolayers and sensitive molecular detection from the deposited region on clothing fabric for the detection of illegal drug substances, a single grain of rice and an orange for pesticide monitoring, and a $100 bill as a potential anti-counterfeit measure, respectively. We believe that our method will provide unique opportunities to expand the utility of colloidal nanoparticles and to greatly improve the accessibility of nanoparticle-based sensing technologies.

PVP-coated gold nanoparticles for the selective determination of ochratoxin A via quenching fluorescence of the free aptamer

This paper describes an aptamer/gold nanoparticle-based assay for ochratoxin A (OTA) detection. This assay is based on the use of an aptamer labeled with carboxyfluorescein (FAM) at its 5'-end and gold nanoparticles (AuNPs) that act as quenchers of fluorescence. When OTA is absent in the system, the fluorescently labeled aptamers are adsorbed on the surface of AuNPs. The fluorescence signal of the fluorescein-labeled OTA aptamer generated is quenched by the fluorescence resonance energy transfer effect of AuNPs. When OTA is present in the system, the fluorescently labeled aptamer binds to OTA and forms a folded structure, which can resist the adsorption of AuNPs. Thus, the fluorescent signal can be retained. The detection limit of this sensing platform is 5 nM, and the linear detection range is 10-1000 nM (R2 = 0.994). The procedure was validated by the quantitation of OTA in spiked ginger powder samples and were found to be free of interference by the sample matrix. The recoveries and the relative standard deviation varied from 89.0% to 117.8% and from 1.9% to 6.3%, respectively.

Low-Cost and Simple Fabrication of Nanoplasmonic Paper for Coupled Chromatography Separation and Surface Enhanced Raman Detection

Surface-enhanced Raman scattering (SERS) is a powerful analytical tool which enables the detection and identification of analytes adsorbed on nanostructured noble metals. However, SERS analysis of complex mixtures can be challenging due to spectral overlap and interference. In this report, we demonstrate a method to simplify the identification of mixed-analyte samples by coupling SERS detection with chromatographic separation on a nanoplasmonic paper substrate. This "nanopaper" substrate is a silver coated glass microfiber filter paper which possesses large SERS enhancement and can serve as a stationary phase in paper chromatography. Nanopaper is easily synthesized using the silver mirror reaction, making it a highly accessible technology. Nanopaper was successfully used as a combined paper chromatography-SERS (PC-SERS) substrate in the separation and identification of mixed organic dyes. It was further employed to separate and identify lycopene and β-carotene in commercial food products, demonstrating the versatility and utility of nanopaper in the identification of complex mixtures.

Multifunctional paper strip based on GO-veiled Ag nanoparticles with highly SERS sensitive and deliverable properties for high-performance molecular detection

The development of paper-based SERS substrates that can allow multi-component detection in real-word scenarios is of great value for applications in molecule detection under complex conditions. Here, a multifunctional SERS-based paper sensing substrate has been developed through the uniform patterning of high-density arrays of GO-isolated Ag nanoparticles on the hydrophilic porous cellulose paper strip (GO@AgNP@paper). Wet-chemical synthesis was used to provide the cover of SERS hot spots on any part of the paper, not just limited surface deposition. In virtue of the inherent ability of paper to deliver analytes by the capillary force, the detection ability of the GO@AgNP@paper substrate was greatly promoted, allowing as low as 10^-19M R6G detection from microliter-volume (50 μL) samples. For the components with different polarity, the paper substrate can be used as an all-in-one machine to achieve the integration of separation and high-sensitive detection for ultralow mixture components, which improves the practical application value of SERS-based paper devices.

Mix-and-match nanobiosensor design: Logical and spatial programming of biosensors using self-assembled DNA nanostructures

The evergrowing need to understand and engineer biological and biochemical mechanisms has led to the emergence of the field of nanobiosensing. Structural DNA nanotechnology, encompassing methods such as DNA origami and single-stranded tiles, involves the base pairing-driven knitting of DNA into discrete one-, two-, and three-dimensional shapes at nanoscale. Such nanostructures enable a versatile design and fabrication of nanobiosensors. These systems benefit from DNA's programmability, inherent biocompatibility, and the ability to incorporate and organize functional materials such as proteins and metallic nanoparticles. In this review, we present a mix-and-match taxonomy and approach to designing nanobiosensors in which the choices of bioanalyte and transduction mechanism are fully independent of each other. We also highlight opportunities for greater complexity and programmability of these systems that are built using structural DNA nanotechnology. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Diagnostic Tools > Biosensing Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Highly effective and chemically stable surface enhanced Raman scattering substrates with flower-like 3D Ag-Au hetero-nanostructures

We demonstrated flower-like 3D Ag-Au hetero-nanostructures on an indium tin oxide glass (ITO glass) for surface enhanced Raman scattering (SERS) applications. The flower-like 3D Ag nanostructures were obtained through electrodeposition with liquid crystalline soft template which is simple, controllable and cost effective. The flower-like 3D Ag-Au hetero-nanostructures were further fabricated by galvanic replacement reaction of gold (III) chloride trihydrate (HAuCl4·3H2O) solution and flower-like Ag. The flower-like Ag-Au hetero-nanostructure exhibited stronger SERS effects and better chemical stability compared with flower-like Ag nanostructure. The localized surface plasmon resonance (LSPR) spectra, field emission scanning electron microscope (FESEM) photos and Ag-Au ratios were studied which show that the surface morphology and shape of the flower-like Ag-Au hetero-nanostructure play significant roles in enhancing SERS. The flower-like 3D Ag-Au hetero-nanostructures fabricated by electrodeposition in liquid crystalline template and galvanic replacement reaction are simple, cheap, controllable and chemical stable. It is a good candidate for applications in SERS detection and imaging.

Nanoplasmonic Alloy of Au/Ag Nanocomposites on Paper Substrate for Biosensing Applications

Plasmonic alloy has attracted much interest in tailoring localized surface plasmon resonance (LSPR) for recent biosensing techniques. In particular, paper-based plasmonic substrates allow capillary-driven lateral flow as well as three-dimensional metal nanostructures, and therefore they become actively transferred to LSPR-based biosensing such as surface-enhanced Raman spectroscopy (SERS) or metal-enhanced fluorescence (MEF). However, employing plasmonic alloy nanoislands on heat-sensitive substrate is still challenging, which significantly inhibits broad-range tailoring of the plasmon resonance wavelength (PRW) for superior sensitivity. Here we report paper-based plasmonic substrate with plasmonic alloy of Au/Ag nanocomposites for highly sensitive MEF and SERS biosensing applications. The nanofabrication procedures include concurrent deposition of Au and Ag below 100 °C without any damage on cellulose fibers. The Au/Ag nanocomposites feature nanoplasmonic alloy with single plasmon peak as well as broad-range tunability of PRW by composition control. This paper-based plasmonic alloy substrate enables about twofold enhancement of fluorescence signals and selective MEF after paper chromatography. The experimental results clearly demonstrate extraordinary enhancement in SERS signals for picomolar detection of folic acid as a cancer biomarker. This new method provides huge opportunities for fabricating plasmonic alloy on heat-sensitive substrate and biosensing applications.

Fluorometric aptamer assay for ochratoxin A based on the use of single walled carbon nanohorns and exonuclease III-aided amplification

The authors describe an aptamer based assay for the food mycotoxin ochratoxin A (OTA). It is based on the use of exonuclease III (Exo III) which assists in signal amplification, and of single-walled carbon nanohorns (SWCNHs) which act as quenchers of fluorescence. The detection scheme employs a hairpin probe (HP) and a signal probe (SP) labeled with carboxyfluorescein (FAM) at its 5'-end. The fluorescence of intact SPs (best measured at excitation/emission wavelengths of 495/518 nm) is quenched by SWCNHs. The HP contains the OTA-specific aptamer sequence and is partially complementary to the SP. After addition of OTA, the aptamer binds OTA and thus exposes a single-stranded sequence that can hybridize with the SP. Exo III digests the SP to liberate the free fluorophore labels. The damaged SPs no longer are adsorbed by the SWCNHs so that fluorescence is no longer quenched. The method has a detection range that is linear from 10 nM to 1000 nM (with a correlation coefficient of 0.997). The limit of detection (LOD), calculated on the basis of a signal to noise ratio of 3, is 4.2 nM. The procedure was validated by the quantitation of OTA in spiked real samples and were found to be free of interference by the sample matrix. Recoveries ranged from 93.8 to 113.0% in beer and from 92.0 to115.9% in red wine. Graphical abstract After adding ochratoxin A (OTA), the aptamer region in hairpin probe (HP) combined with OTA and thus exposed a single-stranded sequence to hybridize with signal probe (SP). Exonuclease III (Exo III) digested SP to liberate the free fluorophore (FAM).

Review of recent research on flexible multifunctional nanopapers

Traditional paper and papermaking have struggled with a declining market during the last few decades. However, the incorporation of nanotechnology into papermaking has brought possibilities to develop low-cost, biocompatible and flexible products with sophisticated functionalities. The functionality of nanopapers emerges from the intrinsic properties of the nanofibrous network, the additional loading of specific nanomaterials (NMs), or the additional deposition and patterning of thin films of nanomaterials on the paper surface. A successful development of functional nanopapers requires understanding how the nanopaper matrix, nanofillers, nanocoating pigments, nanoprinting inks, processing additives and manufacturing processes all interact to provide the intended functionality. This review addresses the emerging area of functional nanopapers. This review discusses flexible and multifunctional nanopapers, NMs being used in nanopaper making, manufacturing techniques, and functional applications that provide new important possibilities to utilize papermaking technology. The interface where NM research meets traditional papermaking has important implications for food packaging, energy harvesting and energy storage, flexible electronics, low-cost devices for medical diagnostics, and numerous other areas.

Clinical Applications of Small-molecule PET Radiotracers: Current Progress and Future Outlook

Radiotracers, or radiopharmaceuticals, are bioactive molecules tagged with a radionuclide used for diagnostic imaging or radiotherapy and, when a positron-emitting radionuclide is chosen, the radiotracers are used for PET imaging. The development of novel PET radiotracers in many ways parallels the development of new pharmaceuticals, and small molecules dominate research and development pipelines in both disciplines. The 4 decades since the introduction of [¹⁸F]FDG have seen the development of many small molecule PET radiotracers. Ten have been approved by the US Food and Drug Administration as of 2016, whereas hundreds more are being evaluated clinically. These radiotracers are being used in personalized medicine and to support drug discovery programs where they are greatly improving our understanding of and ability to treat diseases across many areas of medicine including neuroscience, cardiovascular medicine, and oncology.

Cost-Effective Plasmonic Platforms: Glass Capillaries Decorated with Ag@SiO2 Nanoparticles on Inner Walls as SERS Substrates

A cost-effective method for the fabrication of a glass capillary based plasmonic platform for the selective detection and identification of analytes of importance in health, environment, and safety is demonstrated. This was achieved by coating Ag@SiO₂ nanoparticles (Ag ∼ 60 nm) having silica shell of varying thickness (∼2 and ∼25 nm) on the inside walls of glass capillaries, over 2 cm in length, with uniform coverage. It was found that the particle density on the surface plays a decisive role on the enhancement of Raman signals. Multiple hot spots, which are essentially junctions of amplified electric field, were generated when ∼30 Ag@SiO₂ particles/μm² were bound onto the walls of glass capillaries. The pores of the silica shell allow the localization of analyte molecules to the vicinity of hot spots resulting in signal enhancements of the order of 10¹⁰ (using pyrene as analyte; excitation wavelength, 632.8 nm). The applicability of Ag@SiO₂ coated capillaries for the detection of a wide range of molecules has been explored, by taking representative examples of polyaromatic hydrocarbons (pyrene), amino acids (tryptophan), proteins (bovine serum albumin), and explosives (trinitrotoluene). By increasing the thickness of the silica shell of Ag@SiO₂ nanoparticles, an effective filtration cum detection method has been developed for the selective identification of small molecules such as amino acids, without the interference of large proteins.

Food Quality Monitor: Paper-Based Plasmonic Sensors Prepared Through Reversal Nanoimprinting for Rapid Detection of Biogenic Amine Odorants

This paper describes the fabrication of paper-based plasmonic refractometric sensors through the embedding of metal nanoparticles (NPs) onto flexible papers using reversal nanoimprint lithography. The NP-embedded papers can serve as gas sensors for the detection of volatile biogenic amines (BAs) released from spoiled food. Commercial inkjet papers were employed as sensor substrates-their high reflectance (>80%) and smooth surfaces (roughness: ca. 4.9 nm) providing significant optical signals for reflection-mode plasmonic refractometric sensing and high particle transfer efficiency, respectively; in addition, because inkjet papers have lightweight and are burnable and flexible, they are especially suitable for developing portable, disposable, cost-effective, eco-friendly sensing platforms. Solid silver NPs (SNPs), solid gold NPs (GNPs), and hollow Au-Ag alloyed NPs (HGNs) were immobilized on a solid mold and then transferred directly onto the softened paper surfaces. The particle number density and exposure height of the embedded NPs were dependent on two imprinting parameters: applied pressure and temperature. The optimal samples exhibited high particle transfer efficiency (ca. 85%), a sufficient exposure surface area (ca. 50% of particle surface area) presented to the target molecules, and a strong resonance reflectance dip for detection. Moreover, the HGN-embedded paper displayed a significant wavelength dip shift upon the spontaneous adsorption of BA vapors (e.g., Δλ = 33 nm for putrescine; Δλ = 24 nm for spermidine), indicating high refractometric sensitivity; in contrast, no visible spectroscopic responses were observed with respect to other possibly coexisting gases (e.g., air, N₂, CO₂, water vapor) during the food storage process, indicating high selectivity. Finally, the plasmonic sensing papers were used to monitor the freshness of a food product (salmon).

Plasmonic Schirmer Strip for Human Tear-Based Gouty Arthritis Diagnosis Using Surface-Enhanced Raman Scattering

Biomarkers in tear fluid have attracted much interest in daily healthcare sensing and monitoring. Recently, surface-enhanced Raman scattering (SERS) has enabled highly sensitive label-free detection of small molecules. However, a highly stable straightforward tear assay with superior sensitivity is still under development in tear collection and analysis. Here we report a plasmonic Schirmer strip for on-demand, rapid, and simple identification of biomarkers in human tears. The diagnostic strip features gold nanoislands directly and evenly formed on the top surface of cellulose fibers, which maintain a hygroscopic nature for an efficient collection of tear production as well as provide plasmonic enhancement in SERS signals for identification of tear molecules. The uric acid in human tears was quantitatively detected at physiological levels (25-150 μM) by using SERS. The experimental results also clearly reveal a strong linear correlation between uric acid level in both human tears and blood for gouty arthritis diagnosis. This functional paper strip enables noninvasive diagnosis of disease-related biomarkers and healthcare monitoring using human tears.

Dense AuNP/MoS2 hybrid fabrication on fiber membranes for molecule separation and SERS detection

Synthesis of uniform and dense metal nanostructures on the whole exposed fiber, instead of simply on the membrane surface, is necessary for controllable separation and sensitive SERS detection.

Nuclease-aided target recycling signal amplification strategy for ochratoxin A monitoring

Ochratoxin A (OTA), a toxin produced by Aspergillus ochraceus and Penicillium verrucosum, is one of the most abundant food-contaminating mycotoxins worldwide. OTA mainly exerts nephrotoxicity, immunotoxicity, mutagenicity, carcinogenicity, teratogenicity, and neurotoxicity. This paper describes a simple and sensitive aptamer/single-walled carbon nanohorn (SWCNH)-based assay for OTA detection. SWCNHs can protect DNA from DNase I cleavage. However, aptamers can be detached from the surface of SWCNHs through specific target binding, exposing them to enzymatic cleavage and releases the target for a new cycle. Cycling of targets leads to significant signal amplification and low limit of detection (LOD), resulting in a nearly 20-fold reduction in LOD for OTA assay compared with non-target recycling under the same experimental parameters. This technique responded specifically to OTA without interference from other analogues (Ochratoxin B, Ochratoxin C, warfarin, and N-acetyl-l-phenylalanine). Moreover, the application of this technique in real sample has been verified using red wine samples spiked with a series of OTA concentrations. This aptasensor offers a great practical importance in food safety and can be widely extended for detection of other toxins by replacing the sequence of the recognition aptamer.

Seed-Mediated Hot-Injection Synthesis of Tiny Ag Nanocrystals on Nanoscale Solid Supports and Reaction Mechanism

Controlling the size and shape of noble Ag nanocrystals (NCs) is of great interest because of their unique size- and shape-dependent properties, especially below 20 nm, and because of interesting applications in drug delivery, sensing, and catalysis. However, the high surface energy and tendency of these tiny NCs to aggregate deteriorates their unique properties and limits their applications. To avoid the aggregation of Ag NCs and improve their performance, we report a seed-mediated hot injection approach to synthesize highly dispersed tiny Ag NCs on a nanosized solid CaCO3 support. This simple, low-cost, and effective chemical approach allows for synthesizing highly uniform Ag NCs (∼10 nm) on the surface of presynthesized CaCO3 single NCs (∼52 nm) without any aggregation of the Ag NCs. Viscose fibers were coated with the Ag@CaCO3 composite nanoparticles (NPs) produced, as well as with ∼126 nm Ag NPs for reference. The Ag@CaCO3 composite NPs show excellent UV protection and antibacterial activity against Escherichia coli. In addition, they give a satin sheen gold to a dark gold color to the viscose fibers, while the Ag NPs (∼126 nm) result in a silver color. The proposed synthesis approach is highly versatile and applicable for many other noble metals, like Au or Pt.