Detection of Glioma‐Derived Exosomes with the Biotinylated Antibody‐Functionalized Titanium Nitride Plasmonic Biosensor

Titanium nitride (TiN), as an excellent alternative plasmonic supporting material compared to gold and silver, exhibits tunable plasmonic properties in the visible and near‐infrared spectra. However, label‐free surface plasmon resonance biosensing with TiN is seldom reported due to lack of proper surface functionalization protocols. Herein, this study reports biotinylated antibody‐functionalized TiN (BAF‐TiN) for high‐performance label‐free biosensing applications. The BAF‐TiN biosensor can quantitatively detect exosomes of 30–200 nm extracellular vesicles, isolated from a human glioma cell line. The limit of detection for an exosomal membrane protein with the BAF‐TiN biosensor is found to be 4.29 × 10^?3µg mL^?1 for CD63, an exosome marker, and 2.75 × 10^?3µg mL^?1 for epidermal growth factor receptor variant‐III, a glioma specific mutant protein, respectively. In conclusion, combining the biocompatibility, high stability, and excellent label‐free sensing performance of TiN, the BAF‐TiN biosensor could have great potential for the detection of cancer biomarkers, including exosomal surface proteins.     

Porous Silicon Resonant Microcavity Biosensor for Matrix Metalloproteinase Detection

A real‐time, sensitive, and selective detection device to monitor the healing status of chronic wounds at the point of care is urgently required to render the management of this disease more effective. The photonic properties of porous silicon resonant microcavity (pSiRM) afford an excellent opportunity to be developed as a highly sensitive optical biosensor to monitor the presence of specific biomarkers found in the wound exudate, such as matrix metalloproteinases (MMPs). In this study, the pSiRM is designed, fabricated, and functionalized using a fluorogenic MMP peptide substrate featuring both a fluorophore and a quencher. The peptide‐functionalized pSiRM is then employed as a fluorescence‐based optical biosensor for MMPs. Active MMPs recognize and cleave the peptide sequence of the substrate, producing an immobilized peptide fragment carrying the fluorophore. The fluorescence intensity of the fluorophore embedded within the pSiRM matrix is enhanced by the photonic structure of the pSiRM compared to other pSi photonic structures. This fluorescence enhancement translates into high sensitivity, enabling detection of MMP‐1 at a limit of detection as low as 7.5 × 10^?19 m after only 15 min incubation time. Finally, the biosensor also allows the detection and quantification of the concentration of MMPs in human wound fluid.     

Porous silicon biosensor for detection of variable domain of heavy-chain of HCAb antibody

In this paper, we produce porous silicon (PSi) by electrochemical etching, and it is the first time to evaluate the performance of label-free porous silicon biosensor for detection of variable domain of heavy chain of heavy-chain antibody (VHH). The binding of hen egg white lysozyme (HEWL) and VHH causes a red shift in the reflection spectrum of the biosensor. The red shift is proportional to the VHH concentration in the range from 14 μg . ml-1 to 30 μg . ml-1 with a detection limit of 0.648 ng . ml-1. The research is useful for the development of label-free biosensor applied in the rapid and sensitive determination of small molecules.     

A Conductive Nanowire‐Mesh Biosensor for Ultrasensitive Detection of Serum C‐Reactive Protein in Melanoma

Detection of extracutaneous melanoma is still challenging and is of importance in improving survival rate. In this report, an ultrasensitive biosensor is constructed where a C‐reactive protein (CRP) aptamers based molecular recognition core and a conductive polypyrrole (PPy) nanowire mesh based signal amplifier are developed. The conductive PPy nanowire (less than 10 nm in diameter) mesh architecture is uniformly dispersed within polymeric matrix via template‐free in situ synthesis. Serum CRP levels are quantitatively analyzed through monitoring the conductance change caused by polymeric network shrinkage upon the aptamer‐CRP binding. The limit of detection (LOD) of the polymeric sensor for human CRP sample can reach 7.85 × 10^?19m . This CRP‐specific biosensor and a commercial CRP enzyme‐linked immunosorbent assay (ELISA) kit are used to perform side‐by‐side measurement of serum CRP in melanoma patients. The results indicate that this conductive polymeric senor is highly sensitive and selective in accurately discriminating melanoma patients from healthy controls using serum CRP as a biomarker, which is further validated by a commercial human CRP ELISA kit. Collectively, this novel ultrasensitive nanowire‐based polymeric biosensor may hold promise in biomarker detection and diagnosis of cancer.     

A Universal,Label‐Free,and Sensitive Optical Enzyme‐Sensing System for Nuclease and Methyltransferase Activity Based on Light Scattering of Carbon Nanotubes

A label‐free, enzyme‐responsive nanosystem that uses a DNA/single‐walled carbon nanotube (SWNT) assembly as the substrate is demonstrated for the sensitive, universal detection of restriction and nonrestriction endonucleases as well as methyltransferases in a homogeneous solution on the basis of light scattering (LS) of carbon nanotubes. This protocol is based on the different binding affinities of SWNTs to single‐ and double‐stranded DNA. This difference can lead to different LS signals that can be used for the detection of nuclease cleavage activity. The assay only requires a label‐free oligonucleotide probe, significantly reducing the typical cost. The LS technique and the use of a nuclease‐specific oligonucleotide probe impart extraordinarily high sensitivity and selectivity. This light scattering assay is universal and label‐free with a detection limit of 5 × 10^?6 U μL^?1 for S1 nuclease, 1 × 10^?4 U μL^?1 for EcoRI endonuclease, and 1 × 10^?2 U μL^?1 for EcoRI methylase. In principle, this assay can be used to detect any kind of nuclease by simply changing the DNA sequences of the specific probe.     

Quantum‐Dot‐Functionalized Poly(styrene‐co‐acrylic acid) Microbeads: Step‐Wise Self‐Assembly,Characterization, and Applications for Sub‐femtomolar Electrochemical Detection of DNA Hybridization

A novel nanoparticle label capable of amplifying the electrochemical signal of DNA hybridization is fabricated by functionalizing poly(styrene‐co‐acrylic acid) microbeads with CdTe quantum dots. CdTe‐tagged polybeads are prepared by a layer‐by‐layer self‐assembly of the CdTe quantum dots (diameter = 3.07 nm) and polyelectrolyte on the polybeads (diameter = 323 nm). The self‐assembly procedure is characterized using scanning and transmission electron microscopy, and X‐ray photoelectron, infrared and photoluminescence spectroscopy. The mean quantum‐dot coverage is (9.54 ± 1.2) × 10³ per polybead. The enormous coverage and the unique properties of the quantum dots make the polybeads an effective candidate as a functionalized amplification platform for labelling of DNA or protein. Herein, as an example, the CdTe‐tagged polybeads are attached to DNA probes specific to breast cancer by streptavidin–biotin binding to construct a DNA biosensor. The detection of the DNA hybridization process is achieved by the square‐wave voltammetry of Cd²⁺ after the dissolution of the CdTe tags with HNO₃. The efficient carrier‐bead amplification platform, coupled with the highly sensitive stripping voltammetric measurement, gives rise to a detection limit of 0.52 fmol L^?1 and a dynamic range spanning 5 orders of magnitude. This proposed nanoparticle label is promising, exhibits an efficient amplification performance, and opens new opportunities for ultrasensitive detection of other biorecognition events.     

Immobilization of Quantum Dots in Nanostructured Porous Silicon Films: Characterizations and Signal Amplification for Dual‐Mode Optical Biosensing

Highly sensitive dual‐mode labeled detection of biotin in well‐characterized porous silicon (PSi) films using colloidal quantum dots (QDs) as signal amplifiers are demonstrated. Optimization of the PSi platform for targeted QD infiltration and immobilization is carried out by characterizing and tuning the porosity, film depth, and pore size. Binding events of target QD‐biotin conjugates with streptavidin probes immobilized on the pore walls are monitored by reflective interferometric spectroscopy and fluorescence measurements. QD labeling of the target biotin molecules enables detection based on a distinct fluorescent signal as well as a greater than 5‐fold enhancement in the measured spectral reflectance fringe shift and a nearly three order of magnitude improvement in the detection limit for only 6% surface area coverage of QDs inside the porous matrix. Utilizing the QD signal amplifiers, an exceptional biotin detection limit of ≈6 fg mm^?2 is demonstrated with sub‐fg mm^?2 detection limits achievable.     

Gold Nanoparticle–Colloidal Carbon Nanosphere Hybrid Material: Preparation,Characterization, and Application for an Amplified Electrochemical Immunoassay

A rapid microwave‐hydrothermal method has been developed to prepare monodisperse colloidal carbon nanospheres from glucose solution, and gold nanoparticles (AuNPs) are successfully assembled on the surface of the colloidal carbon nanospheres by a self‐assembly approach. The resulting AuNP/colloidal carbon nanosphere hybrid material (AuNP/C) has been characterized and is expected to offer a promising template for biomolecule immobilization and biosensor fabrication because of its satisfactory chemical stability and the good biocompatibility of AuNPs. Herein, as an example, it is demonstrated that the as‐prepared AuNP/C hybrid material can be conjugated with horseradish peroxidase‐labeled antibody (HRP‐Ab₂) to fabricate HRP‐Ab₂‐AuNP/C bioconjugates, which can then be used as a label for the sensitive detection of protein. The amperometric immunosensor fabricated on a carbon nanotube‐modified glass carbon electrode was very effective for antibody immobilization. The approach provided a linear response range between 0.01 and 250 ng mL^?1 with a detection limit of 5.6 pg mL^?1. The developed assay method was versatile, offered enhanced performances, and could be easily extended to other protein detection as well as DNA analysis.     

Biological reaction signal enhancement in porous silicon Bragg mirror based on quantum dots fluorescence

In this paper, we mainly study the preparation of an optical biosensor based on porous silicon (PSi) Bragg mirror and its feasibility for biological detection. The quantum dot (QD) labeled biotin was pipetted onto streptavidin functionalized PSi Bragg mirror samples, the affinity reaction between QD labeled biotin and streptavidin in PSi occurred, so the QDs were indirectly connected to the PSi. The fluorescence of QD enhanced the signal of biological reactions in PSi. The performance of the sensor is verified by detecting the fluorescence of the QD in PSi. Due to the fluorescence intensity of the QDs can be enhanced by PSi Bragg mirror, the sensitivity of the PSi optical biosensor will be improved.     

Construction and Characterization of Porous SiO2/Hydrogel Hybrids as Optical Biosensors for Rapid Detection of Bacteria

The use of a new class of hybrid nanomaterials as label‐free optical biosensors for bacteria detection (E. coli K12 as a model system) is demonstrated. The hybrids combine a porous SiO₂ (PSiO₂) optical nanostructure (a Fabry–Pérot thin film) used as the optical transducer element and a hydrogel. The hydrogel, polyacrylamide, is synthesized in situ within the nanostructure inorganic host and conjugated with specific monoclonal antibodies (IgGs) to provide the active component of the biosensor. The immobilization of the IgGs onto the hydrogel via a biotin‐streptavidin system is confirmed by fluorescent labeling experiments and reflective interferometric Fourier transform spectroscopy (RIFTS). Additionally, the immobilized IgGs maintain their immunoactivity and specificity when attached to the sensor surface. Exposure of these modified‐hybrids to the target bacteria results in “direct cell capture” onto the biosensor surface. These specific binding events induce predictable changes in the thin‐film optical interference spectrum of the hybrid. Preliminary studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations in the range of 10³–10⁵ cell mL^?1 within minutes.     

Reversible Conversion between Schottky and Ohmic Contacts for Highly Sensitive,Multifunctional Biosensors

Schottky and Ohmic contacts–based electronics play an important role in highly sensitive detection of biomolecules and neural electric impulses, respectively. The reversible conversion between these two contacts appears especially important for multifunctional sensing by just one biosensor. Here, Schottky barrier height (SBH) is successfully tuned by triboelectric nanogenerator (TENG) and the same device is made to achieve reversible conversion between Schottky contact and Ohmic contact. In the same Schottky to Ohmic reversible (SOR) biosensor, highly sensitive detections of biomolecule (i.e., neurotransmitter) and neural electric signal are achieved at different contact states. The SOR biosensor reveals the feasibility of using one device to realize multifunctional detection. This work proposes a simple and significant method to achieve reversible tuning between the Schottky contact and Ohmic contact on one device by TENG, which exhibits great potential in developing multifunctional and high‐sensitivity biosensors, rectifiers, and other functional electronic devices.     

Nanoporous PtRu Alloy Enhanced Nonenzymatic Immunosensor for Ultrasensitive Detection of Microcystin‐LR

A novel nonenzymatic immunosensor for sensitive detection of Microcystin‐LR (MC‐LR) is constructed using a graphene platform combined with mesoporous PtRu alloy as a label for signal amplification. Primary antibody‐Microcystin‐LR (Ab₁) is immobilized onto the surface of a graphene sheet (GS) through an amidation reaction between the carboxylic acid groups attached to the GS and the available amine groups of Ab₁. Mesoporous PtRu alloy, prepared by corrosion PtRuAl alloys, is employed as a label to immobilize secondary antibody (Ab₂). The resulting nanoparticles, PtRu‐Ab₂, are used as labels for the immunosensor to detect MC‐LR. Under optimal conditions, the immunosensor exhibits a wide linear response to MC‐LR that ranges from 0.01 to 28 ng·mL^?1, with a low detection limit of 9.63 pg·mL^?1 MC‐LR. The proposed immunsensor shows good reproducibility, selectivity, and stability. The assayed results of polluted water with the sandwich‐type sensor are acceptable. Importantly, this methodology may provide a promising ultrasensitive assay strategy for other environmental pollutants.     

Cationic Polyelectrolyte Amplified Bead Array for DNA Detection with Zeptomole Sensitivity and Single Nucleotide Polymorphism Selectivity

A highly sensitive strand specific DNA assay, which consists of a peptide nucleic acid (PNA) probe, a cationic conjugated polymer ( PFVP ), and self‐assembled polystyrene beads in microwell arrays on silicon chip, is reported. PFVP , as an efficient signal amplifier and signal reporter, has been specially designed and synthesized to be compatible with commercial confocal microscopes for sensing on solid substrates. The assay operates on the net increase in negative charge at the PNA surface that occurs upon single‐stranded DNA hybridization, which subsequently allows complex formation with the positively charged PFVP to favor energy transfer between the polymer and Cy5‐labeled target. With maximized surface contact provided by bead arrays and signal amplification provided by PFVP , this assay allows detection of ～300 copies of Cy5‐labeled DNA using a commercial confocal microscope. In addition, the same strategy is also extended for label‐free DNA detection with a detection sensitivity of 150 attomole. Excellent discrimination against single nucleotide polymorphism (SNP) is also demonstrated for both Cy5‐labeled and label‐free target detection. This study indicates that cationic conjugated polymers have great potential to be incorporated into the widely used microarray technology for simplified process with improved detection sensitivity.     

Nanoscale Graphene Doped with Highly Dispersed Silver Nanoparticles: Quick Synthesis,Facile Fabrication of 3D Membrane‐Modified Electrode,and Super Performance for Electrochemical Sensing

The performance of graphene‐based hybrid materials greatly depends on the dispersibility of nanoscale building blocks on graphene sheets. Here, a quick green synthesis of nanoscale graphene (NG) nanosheets decorated with highly dispersed silver nanoparticles (AgNPs) is demonstrated, and then the electrospinning technique to fabricate a novel nanofibrous membrane electrode material is utilized. With this technique, the structure, mechanical stability, biochemical functionality, and other properties of the fabricated membrane electrode material can be easily controlled. It is found that the orientations of NG and the dispersity of AgNPs on the surface of NG have significant effects on the properties of the fabricated electrode. A highly sensitive H₂O₂ biosensor is thus created based on the as‐prepared polymeric NG/AgNP 3D nanofibrous membrane‐modified electrode (MME). As a result, the fabricated biosensor has a linear detection range from 0.005 to 47 × 10^?3m (R = 0.9991) with a supralow detection limit of 0.56 × 10^?6m (S/N = 3). It is expected that this kind of nanofibrous MME has wider applications for the electrochemical detection and design of 3D functional nanomaterials in the future.     

Quantum‐Dot‐Tagged Bioresponsive Hydrogel Suspension Array for Multiplex Label‐Free DNA Detection

A novel hydrogel suspension array, which possesses the joint advantages of quantum‐dot‐encoded technology, bioresponsive hydrogels, and photonic crystal sensors with full multiplexing label‐free DNA detection capability is developed. The microcarriers of the suspension array are quantum‐dot‐tagged DNA‐responsive hydrogel photonic beads. In the case of label‐free DNA detection, specific hybridization of target DNA and the crosslinked single‐stranded DNA in the hydrogel grid will cause hydrogel shrinking, which can be detected as a corresponding blue shift in the Bragg diffraction peak position of the beads that can be used for quantitatively estimating the amount of target DNA. The results of the label‐free DNA detection show that the suspension array has high selectivity and sensitivity with a detection limit of 10^?9 M . This method has the potential to provide low cost, miniaturization, and simple and real‐time monitoring of hybridization reaction platforms for detecting genetic variations and sequencing genes.     

A Protein‐Nanocellulose Paper for Sensing Copper Ions at the Nano‐ to Micromolar Level

Tracing heavy metals is a crucial issue in both environmental and medical samples. In this work, a sensing biomolecule, the cyanobacterial C‐phycocyanin (CPC), is integrated into a nanocellulose matrix, and with this, a biosensor for copper ions is developed. The assembly of CPC‐functionalized nanocellulose into a red‐fluorescent, copper‐sensitive hybrid film “CySense”, enhances protein stability and facilitates the reuse and the regeneration of the sensor for several cycles over 7 days. CySense is suitable for the analysis of complex medical samples such as human serum filtrate. The reported biosensor reliably detects copper ion contents with a lower detection limit of 200 × 10^?9m and an IC50 of 4.9 × 10^?6m as changes in fluorescence emission intensity that can be measured with a fluorimeter or a microarray laser scanner.     

A Biosensor Based on Metallic Photonic Crystals for the Detection of Specific Bioreactions

An optical biosensor based on waveguided metallic photonic crystals (MPCs) is reported for the sensitive testing of biomolecular interactions, which provides practical approaches for the label‐free detection of specific bioreactions. The enhancement of the sensitivity or the amplification of the sensor signal by the coupling between the waveguide resonance mode and particle‐plasmon resonance (PPR) breaks through the “bottle‐neck” of the intrinsic response sensitivity defined by the spectral shift of the PPR. The success of this sensor is demonstrated by sensing the specific reaction between the HIV‐1 capsid protein (p24) antigen and the monoclonal anti‐p24 antibody, where the dynamics of the bioreactions can be recorded with a potentially high time resolution. This new sensor stands out due to its compact design and its new physics, compared with conventional devices, its simple operation, the simple fabrication of the MPC chip and the low cost of the whole system.     

A Multiwalled‐Carbon‐Nanotube‐Based Biosensor for Monitoring Microcystin‐LR in Sources of Drinking Water Supplies

A multiwalled carbon nanotube (MWCNT)‐based electrochemical biosensor is developed for monitoring microcystin‐LR (MC‐LR), a toxic cyanobacterial toxin, in sources of drinking water supplies. The biosensor electrodes are fabricated using vertically well‐aligned, dense, millimeter‐long MWCNT arrays with a narrow size distribution, grown on patterned Si substrates by water‐assisted chemical vapor deposition. High temperature thermal treatment (2500 °C) in an Ar atmosphere is used to enhance the crystallinity of the pristine materials, followed by electrochemical functionalization in alkaline solution to produce oxygen‐containing functional groups on the MWCNT surface, thus providing the anchoring sites for linking molecules that allow the immobilization of MC‐LR onto the MWCNT array electrodes. Addition of the monoclonal antibodies specific to MC‐LR in the incubation solutions offers the required sensor specificity for toxin detection. The performance of the MWCNT array biosensor is evaluated using micro‐Raman spectroscopy, including polarized Raman measurements, X‐ray photoelectron spectroscopy, cyclic voltammetry, optical microscopy, and Faradaic electrochemical impedance spectroscopy. A linear dependence of the electron‐transfer resistance on the MC‐LR concentration is observed in the range of 0.05 to 20 μg L^?1, which enables cyanotoxin monitoring well below the World Health Organization (WHO) provisional concentration limit of 1 μg L^?1 for MC‐LR in drinking water.     

High‐κ Solid‐Gate Transistor Configured Graphene Biosensor with Fully Integrated Structure and Enhanced Sensitivity

A fully integrated graphene field‐effect transistor (GFET) nanosensor utilizing a novel high‐κ solid‐gating geometry for a practical biosensor with enhanced sensitivity is presented. Herein, an “in plane” gate supplying electrical field through a 30 nm HfO₂ dielectric layer is employed to eliminate the cumbrous external wire electrode in conventional liquid‐gate GFET nanosensors that undesirably limits the device potential in on‐site sensing applications. In addition to the advantage in the device integration degree, the transconductance level is found to be increased by about 50% over liquid‐gate GFET devices in aqueous‐media, thereby improves the sensitivity performance in sensor applications. As the first demonstration of biosensing applications, a small‐molecule antibiotic, kanamycin A, is detected by means of an aptameric competitive affinity principle. It is experimentally shown that the label‐free and specific quantification of kanamycin A with a concentration resolution at 11.5 × 10^?9 m is achievable through a single direct observation of the 200 s fast bioassay without any further noise canceling. These results demonstrate the utility and practicability of the new devices in label‐free biosensing as a novel analytical tool, and potentially hold great promise in other significant biomedical applications.     

Integration of a Chemical‐Responsive Hydrogel into a Porous Silicon Photonic Sensor for Visual Colorimetric Readout

The incorporation of a chemo‐responsive hydrogel into a 1D photonic porous silicon (PSi) transducer is demonstrated. A versatile hydrogel backbone is designed via the synthesis of an amine‐functionalized polyacrylamide copolymer where further amine‐specific biochemical reactions can enable control of cross‐links between copolymer chains based on complementary target–probe systems. As an initial demonstration, the incorporation of disulfide chemistry to control cross‐linking of this hydrogel system within a PSi Bragg mirror sensor is reported. Direct optical monitoring of a characteristic peak in the white light reflectivity spectrum of the incorporated PSi Bragg mirror facilitates real‐time detection of the hydrogel dissolution in response to the target analyte (reducing agent) over a timescale of minutes. The hybrid sensor response characteristics are shown to systematically depend on hydrogel cross‐linking density and applied target analyte concentration. Additionally, effects due to responsive hydrogel confinement in a porous template are shown to depend on pore size and architecture of the PSi transducer substrate. Sufficient copolymer and water is removed from the PSi transducer upon dissolution and drying of the hydrogel to induce color changes that can be detected by the unaided eye. This highlights the potential for future development for point‐of‐care diagnostic biosensing.