Biological Sensor Applications Research Articles

Targeting G-quadruplex structures with extrinsic fluorogenic dyes: promising fluorescence sensors.

The research on the G-quadruplex DNAs has received much attention in recent years and numerous reports appeared probing their detection, structure, stability, reactivity, selectivity, etc. for the chemical intervention of their biological activity or sensor applications. This feature article provides an account of the recent reports from different research groups on the intriguing fluorescence properties showcased by certain fluorogenic dyes upon their binding to the G-quadruplex DNAs. Aptly, these selective and sensitive emission features demonstrated with structure specific G-quadruplex DNAs have been turned into label-free fluorescence-based detection methods for various metal ions and small biomolecules, down to the pico molar range, having promising bio-analytical applications. While the in vivo formation of G-quadruplexes is dynamically sensitive to the cell cycle, in tandem with the in vitro applications, it is essential to understand the factors that affect chemical, biological and genetic roles of the G-quadruplex structures plausible along the human genome. Towards this, the recent findings on the quantitative visualization of the quadruplex structures in the human cells using immunofluorescent probes open up avenues to explore highly specific quadruplex responsive agents for diagnostic and therapeutic applications, especially to develop a clinically viable method for cancer treatment.

Patterning Anodic Porous Alumina with Resist Developers for Patterned Nanowire Formation

ABSTRACTFormation of patterned metal and semiconductor (e.g. silicon) nanowires is achieved using anodic aluminum oxide (AAO) templates with porous structures of different heights resulting from an initial step difference made by etching the aluminum (Al) thin film with a photoresist developer prior to the anodization process. This approach allows for the growth of vertically aligned nanowire arrays on a metal substrate, instead of an oriented semiconductor substrate, using an electroplating or a chemical vapor deposition (CVD) process. The vertically aligned metal and semiconductor nanowires defined on a metal substrate could be applied to the realization of vertical 3D transistors, field emission devices, or nano-micro sensors for biological applications.

Development of phase detection schemes based on surface plasmon resonance using interferometry.

Surface plasmon resonance (SPR) is a novel optical sensing technique with a unique ability to monitor molecular binding in real-time for biological and chemical sensor applications. Interferometry is an excellent tool for accurate measurement of SPR changes, the measurement and comparison is made for the sensitivity, dynamic range and resolution of the different analytes using interferometry techniques. SPR interferometry can also employ phase detection in addition to the amplitude of the reflected light wave, and the phase changes more rapidly compared with other approaches, i.e., intensity, angle and wavelength. Therefore, the SPR phase interferometer offers the advantages of spatial phase resolution and high sensitivity. This work discusses the advancements in interferometric SPR methods to measure the phase shifts due to refractive index changes. The main application areas of SPR sensors are demonstrated, i.e., the Fabry-Perot interferometer, Michelson interferometer and Mach-Zehnder interferometer, with different configurations. The three interferometers are discussed in detail, and solutions are suggested to enhance the performance parameters that will aid in future biological and chemical sensors.

Dynamic plasmonic beam shaping by vector beams with arbitrary locally linear polarization states

Vector beams, which have space-variant state of polarization (SOP) comparing with scalar beams with spatially homogeneous SOP, are used to manipulate surface plasmon polarizations (SPPs). We find that the excitation, orientation, and distribution of the focused SPPs excited in a high numerical aperture microscopic configuration highly depend on the space-variant polarization of the incident vector beam. When it comes to vector beam with axial symmetry, multi-foci of SPPs with the same size and uniform intensity can be obtained, and the number of foci is depending on the polarization order n. Those properties can be of great value in biological sensor and plasmonic tweezers applications.

Fluorescence enhancement of cadmium selenide quantum dots assembled on silver nanoparticles and its application to glucose detection.

In this work, a new assembled glucose sensor based on the Ag nanoparticle (AgNP)-enhanced fluorescence of CdSe quantum dots (QDs) was developed. The mercaptoglycerol-modified AgNPs and aminophenylboronic acid-functionalized CdSe QDs are assembled into AgNP-CdSe QD complexes through the formation of a boronate ester bond. As compared to that of bare CdSe QDs, up to a 9-fold fluorescence enhancement and a clear blue shift of the emission peak for AgNP-CdSe QD complexes were observed, which is attributed to the surface plasmon resonance of AgNPs. In addition, the as-formed complexes are gradually disassembled in the presence of glucose molecules because they can replace the AgNPs by competitive binding with boronic acid groups, resulting in the weakening of fluorescence enhancement. The decrease in fluorescence intensity presents a linear relationship with glucose concentration in the range from 2 to 52 mM with a detection limit of 1.86 mM. Such a metal-enhanced QDs fluorescence system may have promising applications in chemical and biological sensors.

Fabrication of 1D ZnO nanostructures on MEMS cantilever for VOC sensor application

This study reports the fabrication method and sensing performance for novel 1D zinc oxide (ZnO) nanorods and nanotubes grown on nickel MEMS cantilevers. The fabrication of the nanostructures and the cantilevers are simple and low-cost using standard lithography, electrodeposition, and hydrothermal etching processes. 1D ZnO nanostructures increase the total sensitive area for biological and chemical sensor applications. We performed experiments with various VOCs with a real-time sensor system developed in our laboratory. While Ni microcantilevers produced no signal, ZnO nanostructure coated microcantilevers showed good sensitivity and repeatable changes. Furthermore, the nanotube coated microcantilevers showed more than 10 fold increase in sensitivity compared to the nanorod coated microcantilevers which can be explained to the fact that ZnO nanotubes have higher surface area and subsurface oxygen vacancies and these provide a larger effective surface area with higher surface-to-volume ratio as compared to ZnO nanorods. The tests are performed using dynamic mode of operation near resonant frequency using magnetic actuation and optical sensing. The phase stability and the limit of detection of ZnO nanotube coated microcantilevers exposed to diethylamine (DEA) were 0.02° and lower than 10ppm, respectively. ZnO nanostructure coated microcantilevers have good potential for VOC sensor applications especially for amine groups.

Poly(N-isopropylacrylamide) Surfactant-Functionalized Responsive Silver Nanoparticles and Superlattices

Metal nanoparticles exhibit unique optical characteristics in visible spectra produced by local surface plasmon resonance (SPR) for a wide range of optical and electronic applications. We report the synthesis of poly(N-isopropylacrylamide) surfactant (PNIPAM-C18)-functionalized metal nanoparticles and ordered superlattice arrays through an interfacial self-assembly process. The method is simple and reliable without using complex chemistry. The PNIPAM-C18-functionalized metal nanoparticles and ordered superlattices exhibit responsive behavior modulated by external temperature and relative humidity (RH). In situ grazing-incidence small-angle X-ray scattering studies confirmed that the superlattice structure of PNIPAM-C18 surfactant-functionalized nanoparticle arrays shrink and spring back reversibly based on external thermal and RH conditions, which allow flexible manipulation of interparticle spacing for tunable SPR. PNIPAM-C18 surfactants play a key role in accomplishing this responsive property. The ease of fabrication of the responsive nanostructure facilitates investigation of nanoparticle coupling that depends on interparticle separation for potential applications in chemical and biological sensors as well as energy storage devices.

Imparting Tunable and White-Light Luminescence to a Nanosized Metal–Organic Framework by Controlled Encapsulation of Lanthanide Cations

An alternative way was demonstrated to fabricate highly luminescent MOFs and white-light emitter by encapsulating lanthanide(III) (Ln(3+)) cations into the channels of Al-MIL-53-COOH (1) nanocrystals. The framework can serve as both a host and an antenna for protecting and sensitizing the luminescence of the Ln(3+) cations. PXRD, TEM, FTIR, TGA, and N2 adsorption measurements were performed to determine the structure, thermal stability, and BET surface area of the obtained products. The Ln(3+)-incorporated nanocrystals show strong emission under UV-light irradiation, and their luminescent properties were systematically studied. In contrast to the essentially unchangeable luminescence of lanthanide-based MOF, the luminescence of Ln(3+) @1 allows design and tuning. The versatile luminescence, good thermal stability, nanometer size, and compatibility with aqueous condition reveal these materials may have potential applications in LED lamps, barcoded materials, and biological sensors. In addition, the thin films of Ln(3+)@1 were prepared by chemical solution deposition (CSD) from their metastabilized colloidal solutions, which open the way to practical applications such as pellets and sensors for vapors.

Dual-Band Coherent Perfect Absorption/Thermal

Dual-band perfect absorption/thermal emission is shown to be a general property of an ultrathin bilayer consisting of a dielectric and a totally reflective layer if the permittivity of the dielectric can be described by Drude-Lorentz (DL) model. The two bands coexist and reside on opposite sides of the Lorentzian resonant frequency where the material loss is small. However, the perfect absorption mechanism for the two bands is distinguishably different. One band is related to Fabry-Perot phenomenon and the surge of refractive index near the Lorentzian resonance. This band is polarization insensitive. The other band is associated with excitation of Brewster-type mode at the ϵ-near-zero (ENZ) wavelength and occurs only for p-polarized wave at oblique incidences. This mode has a fast-wave non-radiative character and propagates along the ultrathin ENZ layer superimposed on the highly reflective surface. Both bands exhibit wide-angle high emission with a small shift in their center frequencies which can be tuned by tuning the Lorentzian resonance. The resonance-enhanced dual band absorption occurs in the ultrathin DL layer at the weakly absorbing wavelengths as a consequence of an interaction between the total transmission and the total reflection. We demonstrate this phenomenon in a silicon carbide/copper bilayer. The suggested structure may have applications in biological and chemical sensors, IR sensors, thermal emission controls, thermophotovoltaics, and photodetectors.

A large-area and contamination-free graphene transistor for liquid-gated sensing applications

We present a simple, low-cost, large area, and contamination-free monolayer graphene field-effect transistor for liquid-gated sensing applications. The graphene surface does not require any photoresist including the commonly used polymethylmethacrylate, thus avoiding possible contamination and mobility degradation. We also examine the effects of different etching solutions and concentrations on the Dirac point of graphene. With optimal device fabrication recipe, we demonstrate the device's capability to sense different KCl concentrations and pH values under liquid gating configuration. Additionally, using polydimethylsiloxane as substrates holds an advantage of enabling simple integration between microfluidic systems and graphene for chemical and biological sensor applications.

High Performance of Silicon Nanowire-Based Biosensors using a High-k Stacked Sensing Thin Film

High performance silicon nanowire (SiNW) sensors with SiO2/HfO2/Al2O3 (OHA) engineered sensing thin films were fabricated. A lower interface state density, a larger capacitance and a stronger chemical immunity, which are essential for enhancing the performance of devices, were accomplished by stacking thin SiO2, HfO2, and Al2O3 layers, respectively, in sequence on the SiNW channel. Compared with the conventional single SiO2 thin film, the staked OHA thin films demonstrated improved sensing performances; a higher sensitivity, a lower hysteresis voltage, and a smaller drift rate, as well as a higher output current. Therefore, the SiNW sensors with OHA stacked sensing thin films are very promising to biological and chemical sensor applications.

Highly Efficient Wettability Control via Three-Dimensional (3D) Suspension of Titania Nanoparticles in Polystyrene Nanofibers

Electrospinning is a simple and highly versatile method for the large-scale fabrication of polymeric nanofibers. Additives or fillers can also be used to functionalize the nanofibers for use in specific applications. Herein, we demonstrate a novel and efficient way to fabricate superhydrophobic to hydrophilic tunable mats with the combined use of electrospinning and electrospraying that may be suitable for mass production on the merits of rapid deposition. The tunable nanocomposite mats were comprised of hydrophobic polystyrene nanofibers and hydrophilic titania nanoparticles. When the electrical conductivity of the electrospinning solution was increased, the surface morphology of the mats changed noticeably from a bead-on-string structure to an almost bead-free structure. Polystyrene (PS)-titania nanocomposite mats initially yielded a static water contact angle as high as 140° ± 3°. Subsequently exposing these mats with relatively weak ultraviolet irradiation (λ = 365 nm, I = 0.6 mW/cm²) for 2 h, the unique 3D suspension of the photoactive titania nanoparticles maximized the hydrophilic performance of the mats, reducing the static water contact angle to as low as 26° ± 2°. The tunable mats were characterized by scanning electron microscopy (SEM), static water contact angle (WCA) measurements, and energy-dispersive X-ray spectroscopy (EDX). Our findings confirmed that the tunable mats fabricated by the simultaneous implementation of electrospraying and electrospinning had the most efficient ultraviolet (UV)-driven wettability control in terms of cost-effectiveness. Well-controlled tunable hydrophobic and hydrophilic mats find potential applications in functional textiles, environmental membranes, biological sensors, scaffolds, and transport media.

Current Trends in Carbon Nanotubes and Their Applications

Carbon based nanostructure materials exhibit unique mechanical, electrical, and optical characteristics, which may result in many unique device designs. These materials are biocompatible, chemically inert but capable of altering their electronic properties in the presence of some chemical species, and dimensionally compatible with biomolecules. They have interesting electronic characteristics, thus rendering them as potential chemical and biosensors. The recent progress in nanostructured materials and their possible applications in chemical and biological sensors could have a significant impact on data collection, processing, and recognition. This investigation is aimed towards evaluating the applications of nano-structures of carbon and giving a consolidated view of the structure, properties and applications of carbon nanotubes, with the aim of drawing attention to useful available information and to enhancing the interest in this new highly advanced technological field for the researcher and the manufacturing engineer.

Facile Synthesis and Characterization of Au Nanoclusters‐Silica Fluorescent Composite Nanospheres

We developed a novel method for the synthesis of Au nanoclusters (NCs) silica fluorescent composite nanospheres by mixing the as‐prepared bovine serum albumin (BSA) protected Au NCs with amino‐modified silica spheres in acetate buffer solution. The products were characterized by high‐resolution transmission electron microscopy (HRTEM), X‐ray photoelectron spectroscopy (XPS), fluorescent microscope imaging (FLMI), and dynamic light scattering (DLS) measurements. The proposed method was simple, efficient, and inexpensive. In addition, the composite nanospheres exhibited favorable water‐dispersible, stable, and fluorescent properties, potentially leading to further applications in chemical and biological sensors. A reasonable mechanism was also proposed for the formation of composite nanospheres.

Hydrogen storage and release by bending carbon nanotubes

Efficient storage of hydrogen at room temperature is a bottleneck problem for hydrogen-based energy applications. A simple way of hydrogen storage and release by bending carbon nanotubes (CNTs) at room temperature is demonstrated using molecular dynamics (MD) simulations. A large number of hydrogen molecules can be put in CNTs at low temperatures, and then the hydrogen molecules can be completely encapsulated in the CNTs by bending the CNTs to a critical angle. The critical angle decreases with increasing CNT length, while it increases with increasing hydrogen number and temperature. However, the CNT chirality has a negligible influence on the critical angle and hydrogen storage process. It is demonstrated that the release of the hydrogen molecules also can be controlled accurately at room temperature by changing bending angle. The van der Waals force plays an important role in the hydrogen storage and release process. Compared with the conventional methods for hydrogen storage, the brand-new one occurs at room temperature and the release of the hydrogen molecules can be controlled accurately by changing bending angle. Besides, the special structure of the bent CNTs will also significantly enhance their applications in atomic storage, various chemical and biological sensors and actuators, catalyst and catalyst supports, nanoelectronic devices as well as high-capacity energy storage in solar cells or fuel cells.

Porous Silicon Based Protocol for the Rapid and Real-Time Monitoring of Biorecognition Between Human IgG and Protein A Using Functionalized Superparamagnetic Beads

Optical interferometer biosensors based on porous silicon (PSi) are being studied for chemical and biological sensor applications. In particular, single PSi is a promising sensing platform for biomolecules and based on monitoring changes in the optical thickness (2nL) from Fabry-Perot fringes due to magnetic particle-labels covering PSi surfaces. These methods offer a fast, and one-step method for immunoassaying by combining nano-sized superparamagnetic beads (SPBs) with interferometer PSi platforms. Furthermore, SPBs covered with biomolecules have a higher reflective index than the biomolecules alone, which results in larger shifts of the optical thickness (2nL) by the penetration of SPBs inside pore walls of PSi. In this work, we immobilized protein A onto macropore PSi and used optical reflection to detect human IgG immobilized onto nano-sized SPBs by measuring changes of optical thickness (2nL). Furthermore, the optical thickness (2nL) was proportional to mass of the biomolecules, thus the Δ2nL corresponded to the mass fraction of active IgG with SPBs inside PSi pores. Therefore, we quantified the changes of optical thickness (2nL) to enable the detection of SPBs functionalized human IgG based on protein-A modified macropore sized PSi platform.

Facile fabrication of conducting polymer nanowire based field effect transistor with controlled shape and position

Graphical abstractDisplay Omitted Highlights? Single conducting polymer nanowire is fabricated directly on the device platform. ? Facile method provids the controlled position, width, and length of nanowire. ? Nanowire is electrochemically deposited on the nanopatterned area of electrode. ? Polypyrrole nanowire based field effect transistor is successfully established. In this paper, a facile method by which conducting polymer nanowire can be fabricated directly on the device platform in controlled position, width, and length is proposed. Conducting polymer was electrochemically deposited on the nanopatterned area of a working electrode. The shape and position of the nanowire, in particular the length of the nanowire can be easily controlled by modulation of the nanopatterned area via lithography method. Through the proposed fabrication method, a polypyrrole nanowire based field effect transistor was successfully established. This fabrication design provides an easy way to manufacture the conducting polymer nanowire based devices in controlled manner, and the devices are suitable for application in chemical and biological sensors as well as organic electronics.

Cationic Polyfluorene-b-Neutral Polyfluorene “Rod–Rod” Diblock Copolymers

All-conjugated “rod–rod” diblock copolymers are an emerging class of polymeric materials of considerable interest for applications in chemical and biological sensors or as components for optoelectronic devices. Here, we report a novel cationic diblock copolymer containing a neutral polyalkylfluorene block covalently bound to a polar polyfluorene counterpart—poly[9,9-bis(6-trimethylammoniumhexyl)-2,7-fluorene]-b-poly(3-hexyl-2,5-thiophene) (PF6NBr-b-PF8)—which was synthesized in a sequential Suzuki–Miyaura polymerization and was made ionic with trimethylamine in a subsequent quaternization step. The optical properties of this material were investigated by UV/vis and photoluminescence spectroscopies in three different solvents: methanol, THF and THF/methanol 1:1. Atomic force microscopic (AFM) imaging experiments provided evidence for solvent-induced aggregation. The formation of vesicles and spherical particles is observed in layers from THF and methanolic solution.

Organic Thin‐Film Transistors for Chemical and Biological Sensing

Organic thin-film transistors (OTFTs) show promising applications in various chemical and biological sensors. The advantages of OTFT-based sensors include high sensitivity, low cost, easy fabrication, flexibility and biocompatibility. In this paper, we review the chemical sensors and biosensors based on two types of OTFTs, including organic field-effect transistors (OFETs) and organic electrochemical transistors (OECTs), mainly focusing on the papers published in the past 10 years. Various types of OTFT-based sensors, including pH, ion, glucose, DNA, enzyme, antibody-antigen, cell-based sensors, dopamine sensor, etc., are classified and described in the paper in sequence. The sensing mechanisms and the detection limits of the devices are described in details. It is expected that OTFTs may have more important applications in chemical and biological sensing with the development of organic electronics.

Biocompatible hydroxyapatite nanoparticles as a redox luminescence switch

A redox luminescence switch was prepared by doping hydroxyapatite nanoparticles with CePO(4):Tb. The resulting multifunctional material exhibits good biocompatibility, biological affinity, and potential drug-carrying capability. The luminescent hydroxyapatite nanoparticles may find important applications in biomedical diagnostics, drug delivery, and biological sensors.