Real-time Label-free Detection Research Articles

Analytical modeling and performance assessment of high performance split-gate dielectric modulated InGaAs GAA junctionless MOSFET biosensor

In this manuscript, split gate dielectric modulated gate-all-around junctionless metal oxide field-effect transistor (SG-GAA-JLFET) based on III-V compound (InGaAs) has recently come forward as a potentiated device in biosensors design due to ultra-sensitivity, selectivity & real-time label-free detection capabilities. In this paper, the boundary conditions at the edges of the junctions are discussed, and their consequences on the Analytical modeling in GAA-JLFET are investigated. The channel-center potential equation is computed by evaluating 2-D Poisson's equation based on the parabolic-potential technique. Additionally, the change of device dimensional parameters upon biosensor sensitivity is computed to investigate the dielectric modulation effects for neutral and charge biomolecules, per se. A SILVACO TCAD simulation tool is utilized for verification and validation of the proposed analytical model. The sensitivity metric of the neutral analyte with a higher dielectric constant is found raised. The value of surface potential sensitivity for Gelatin (k = 12) is seen as 72 which is proportionately 31%, 60%, and 200% greater compared to the sensitivity of apomyoglobin (k = 8), Bacteriophage T7 (k = 6.3), as well as Glucose Oxidase (k = 3.46) for cavity length equal to 20 nm.

Study and Design of a Machine Learning-Enabled Laser-Based Sensor for Pure and Sea Water Determination Using COMSOL Multiphysics

Accurate detection of salt in water is crucial in many applications. Numerous techniques, using direct and indirect methods, have been employed to design seawater sensors. Among the indirect sensing methods, optical sensors are known to be the most accurate, easy to implement, and suitable for application where the chemical properties of the solution to be tested should stay unchanged. This research presents a novel method for real-time label-free biochemical detection of salty water combining various optics concepts with a machine learning system. COMSOL Multiphysics has been employed to design and simulate the proposed sensor. The designed device uses a laser light emitted from the top of a water container, with a sensing part located on the bottom surface. The laser light initially propagates in the air portion, then refracts when it comes into contact with the air-water interface. Different parameters, including the laser beam wavelength λ and its incident angles θi, the temperature, and the air-water levels are employed to generate a set of data and the multilayer perceptron classifier (MLP) to model prediction. The obtained results validated the concept of the proposed sensor using machine learning. The sensor’s prediction precision under various temperature conditions is R2 = 0.844, the equivalent of an MSE of 0.155.

Fiber Optic Plasmonic Sensors Based on Nanodome Arrays with Nanogaps.

In this study, a high-performance fiber optic surface plasmon resonance (FO-SPR) sensor using a dome array with nanogaps (DANG) is proposed for label-free real-time detection of biomolecules. A novel and simple method using polymer beads enables high sensitivity by allowing hotspots with nanometer spacing between the Au dome and the surrounding film. The nanodome structure, which comprises a polymer core and a Au shell, induces a localized surface plasmon, expands the sensing area, and extensively enhances the electromagnetic field. The refractive index sensitivity of the FO-SPR sensor with nanostructures, i.e., with nanogaps and nanodomes, was found to be 7.8 times higher than that of the FO-SPR sensor without nanostructures. The proposed sensor achieved a low detection limit of 38 fg/mL while quantifying thyroglobulin antibody-antigen interactions and exhibited excellent selectivity. In addition, it helped detect serum samples with a 103% recovery rate.

Enhanced sensing performance from trapezoidal metallic gratings fabricated by laser interference lithography.

Nanograting-based plasmonic sensors are widely regarded as promising platforms due to their real-time label-free detection and ease of integration. However, many reported grating structures are too complicated to fabricate, which limits their application. We propose a 1D bilayer metallic grating with trapezoidal profile as a near-infrared plasmonic sensor in the spectral interrogation. Trapezoidal gratings tend to perform better than rectangular gratings as sensors, particularly as they can detect at oblique incidence to obtain higher performance. Furthermore, we have successfully fabricated such a grating with a period of 633 nm over a 2.25 cm2 area using a two-step approach based on laser interference lithography. Glucose detection has been conducted to experimentally validate the sensing performance of the as-prepared grating. The measured sensitivity and figure-of-merit can reach up to 786 nm/RIU and 30, respectively. Our research sheds new light on the development of cost-effective sensing devices.

Real-time label-free detection of DNA hybridization using a functionalized graphene field effect transistor: a theoretical study.

Detection of DNA hybridization with high sensitivity and accuracy plays a major role in clinical diagnosis and treatment. Despite intense experimental studies of graphene field effect transistor as DNA hybridization detector, the mechanism of detection and changes in the electrical properties of the device is not investigated in detail. To this end, we have investigated an armchair graphene nanoribbon (AGNR) interconnected between gold electrodes as a detector of DNA hybridization. Using non-equilibrium Green’s function method and density functional theory, the effect of 1-pyrenebutanoic acid succinimidyl ester (PBASE) linker, probe, and target DNA on the electrical properties of the device has been investigated at zero bias voltage. The results show that, after functionalization of AGNR with PBASE, the conductance of the device increases while functionalization with probe and target DNA leads to a decrease in conductance. The changes in the projected density of states on the AGNR and transmission around Fermi energy are the reason for the change in conductance of the system. In all cases, both charge transfer and electrostatic gating are responsible for the change in the electrical properties of the system. The results show that our device detects DNA hybridization with a sensitivity of 10% at zero bias voltage, and by applying a suitable gate voltage, it can show higher sensitivity.Graphical abstract

Joint optimization of quality factor and sensitivity: Research on the performance quantification of two dimensional photonic crystal biosensor

The two dimensional (2D) photonic crystal (PC) biosensor based on resonant refractive index (RI) sensing has been widely studied due to its high quality factor, strong anti-interference ability, label-free real-time detection and easy integration. However, there is no unified mechanism to compare various PC slab biosensors based on different sensing principles and biological detection targets. Here, we first briefly introduced the definition of detection limit (DL) that is widely accepted, including influence factors such as signal-to-noise ratio, system resolution, and temperature drift. Then, this article focused on calculating and analyzing the influence of quality factor (Q) and sensitivity on DL, and proposed the optimal Q and sensitivity intervals for obtaining extremely low DLs, hoping to provide design strategies for improving the performance of other 2D PC biosensors. Finally, according to the optimal intervals, we performed a joint optimization of Q and sensitivity for the linewidth modulation cavity suitable for the specific detection of small biological targets, and obtained a relatively ideal DL.

Optical Monitoring of the Production Quality of Si-Nanoribbon Chips Intended for the Detection of ASD-Associated Oligonucleotides.

Gas-phase etching and optical lithography were employed for the fabrication of a silicon nanoribbon chip (Si-NR chip). The quality of the so-fabricated silicon nanoribbons (Si-NRs) was monitored by optical Raman scattering spectroscopy. It was demonstrated that the structures of the Si-NRs were virtually defect-free, meaning they could be used for highly sensitive detection of biological macromolecules. The Si-NR chips were then used for the highly sensitive nanoelectronics detection of DNA oligonucleotides (oDNAs), which represent synthetic analogs of 106a-5p microRNA (miR-106a-5p), associated with the development of autism spectrum disorders in children. The specificity of the analysis was attained by the sensitization of the Si-NR chip sur-face by covalent immobilization of oDNA probes, whose nucleotide sequence was complementary to the known sequence of miR-106a-5p. The use of the Si-NR chip was demonstrated to al-low for the rapid label-free real-time detection of oDNA at ultra-low (~10−17 M) concentrations.

Dual-optofluidic waveguide in-line fiber biosensor for real-time label-free detection of interferon-gamma with temperature compensation.

Temperature cross-sensitivity is a long-standing challenge for most of the in-line fiber optofluidic waveguide biosensors. In this paper, we propose a dual-optofluidic waveguide antiresonant reflecting optical waveguide (ARROW) biosensor for the detection of interferon-gamma (IFN-γ) concentration with temperature compensation. Two Fabry-Perot resonators infiltrated with IFN-γ and NaCl were formed in a hollow core fiber, which generate two resonance dips based on the ARROW model. The optical biosensor for the detection of interferon-gamma (IFN-γ) has been a key research interest in recent years because IFN-γ is an important early biomarker for many serious human diseases. Based on the dual-optofluidic waveguide ARROW biosensor, the IFN-γ concentration can be measured through the modulation of the resonance condition of the ARROW, while the temperature fluctuation can be eliminated due to same thermo-optic coefficients of two infiltration liquids. The experimental results show that the response of the ARROW biosensor can be amplified significantly with the signal-enhanced streptavidin, and the limit of detection of 0.5 ng/ml can be achieved for the IFN-γ concentration. More importantly, the influence of the temperature could be compensated through the referenced resonance dip. The proposed fiber biosensor has a great potential for the real-time detection of IFN-γ concentrations in the fields of health monitoring, cancer prevention, biological engineering, etc.

Label-Free Detection of Protein Tyrosine Phosphatase 1B (PTP1B) by Using a Rationally Designed Förster Resonance Energy Transfer (FRET) Probe.

A highly selective detection method of native protein tyrosine phosphatase 1B (PTP1B) is described using a target specific probe equipped with 1-naphthylamine (λex =330 nm, λem =445 nm). Irradiation of a mixture of PTP1B and Probe 1 with ultraviolet light of 280 nm (corresponding to PTP1B excitation maximum) resulted in significant fluorescence increase at 445 nm, following FRET characteristics. This phenomenon does not occur with other closely related phosphatases or cellular abundant alkaline phosphatase (APP). Probe 1, the most potent and selective probe, was found to competitively inhibit PTP1B (Ki ≈42 nm), whereas APP inhibition was found to be in the low micromolar range. Furthermore, Probe 1 discriminates between PTP1B and several other phosphatases. Here, we report real-time label-free FRET detection of pure PTP1B as well as induced human PTP1B in Escherichia coli cell lysate. In contrast to 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP), a representative fluorescence turn-on PTP substrate, our FRET probe successfully differentiated human cervical carcinoma cell lysate, SiHa, which has a high expression level of PTP1B, from PTP1B-knockdown SiHa cell lysate (that is, siRNA was used for PTP1B knockdown).

Graphene–MoS2–metal hybrid structures for plasmonic biosensors

Abstract Surface Plasmon Resonance (SPR) biosensors are widely used for real-time label-free detection in medical diagnostics, pharmaceutical researches and food safety. Although there is a growing interest in miniaturization of biosensors for self-detection and diagnostics at out of laboratory, the performance of conventional metal SPR sensors is still limited. In this paper, we propose graphene–MoS 2 – metal hybrid structures based plasmon sensors under the best minimum light intensity approach, which represents the performance analysis in case of the lowest reflected light strength. It is demonstrated that the metal thickness can be reduced from 55 nm to 32 nm and 37 nm meanwhile the performance of the background sensor can be improved by 87% and 13% with the 4 additional MoS2 and graphene layers, respectively. We show that MoS2 based SPR devices provide much better sensitivity performance than graphene based devices. Our results reveal the another promising property of MoS2: The sensitivity of SPR sensors can be greatly increased with a few number of MoS2 within the angular SPR system while reducing the size of the device, especially for particular applications such as detecting a single molecule and biosensing at low biomolecule concentration. Furthermore, we show that the equivalent optical properties of multilayered nanostructures also depend on the layer thickness which is a novel knowledge for the next studies on 2D material based SPR plasmonic devices.

Label-free real-time detection of biotinylated bovine serum albumin using a low-cost optical cavity-based biosensor.

We have developed a low-cost optical cavity-based biosensor with a differential detection method for point-of-care medical diagnostics. To experimentally demonstrate its label-free real-time biosensing capability, we performed the detection of biotinylated bovine serum albumin (BSA). Streptavidin is introduced into the optical cavity structure and immobilized on 3-aminopropyltriethoxysilane (APTES) coated surface. After rinsing out unbound streptavidin with DI water, biotinylated BSA without any labeling is introduced. A CMOS camera captures the transmitted light of two different wavelengths passing through the optical cavity sensing area in real-time. Then, the differential values are calculated to enhance the responsivity. We successfully demonstrated the label-free real-time detection of biotinylated BSA, and the measurement results matched well with the simulation results. The limit of detection of the optical cavity-based biosensor for the biotinylated BSA detection with the sensing area of 180 μm × 180 μm is estimated to be 2.82 pM, which could be reduced further for a smaller sensing area with the tradeoff of a longer sensing time.

Low-Power Optical Trapping of Nanoparticles and Proteins with Resonant Coaxial Nanoaperture Using 10 nm Gap.

We present optical trapping with a 10 nm gap resonant coaxial nanoaperture in a gold film. Large arrays of 600 resonant plasmonic coaxial nanoaperture traps are produced on a single chip via atomic layer lithography with each aperture tuned to match a 785 nm laser source. We show that these single coaxial apertures can act as efficient nanotweezers with a sharp potential well, capable of trapping 30 nm polystyrene nanoparticles and streptavidin molecules with a laser power as low as 4.7 mW. Furthermore, the resonant coaxial nanoaperture enables real-time label-free detection of the trapping events via simple transmission measurements. Our fabrication technique is scalable and reproducible, since the critical nanogap dimension is defined by atomic layer deposition. Thus our platform shows significant potential to push the limit of optical trapping technologies.

A label-free nanostructured plasmonic biosensor based on Blu-ray discs with integrated microfluidics for sensitive biodetection

Nanostructure-based plasmonic biosensors have quickly positioned themselves as interesting candidates for the design of portable optical biosensor platforms considering the potential benefits they can offer in integration, miniaturization, multiplexing, and real-time label-free detection. We have developed a simple integrated nanoplasmonic sensor taking advantage of the periodic nanostructured array of commercial Blu-ray discs. Sensors with two gold film thicknesses (50 and 100nm) were fabricated and optically characterized by varying the oblique-angle of the incident light in optical reflectance measurements. Contrary to the use normal light incidence previously reported with other optical discs, we observed an enhancement in sensitivity and a narrowing of the resonant linewidths as the light incidence angle was increased, which could be related to the generation of Fano resonant modes. The new sensors achieve a figure of merit (FOM) up to 35 RIU−1 and a competitive bulk limit of detection (LOD) of 6.3×10−6 RIU. These values significantly improve previously reported results obtained with normal light incidence reflectance measurements using similar structures. The sensor has been combined with versatile, simple, ease to-fabricate microfluidics. The integrated chip is only 1cm2 (including a PDMS flow cell with a 50µm height microfluidic channel fabricated with double-sided adhesive tape) and all the optical components are mounted on a 10cm×10cm portable prototype, illustrating its facile miniaturization, integration and potential portability. Finally, to assess the label-free biosensing capability of the new sensor, we have evaluated the presence of specific antibodies against the GTF2b protein, a tumor-associate antigen (TAA) related to colorectal cancer. We have achieved a LOD in the pM order and have assessed the feasibility of directly measuring biological samples such as human serum.

Wavelength shift in a whispering gallery microdisk due to bacterial sensing: A theoretical approach

Whispering gallery mode microcavities have recently been studied as a means to achieve real-time label-free detection of biological targets such as virus particles, specific DNA sequences, or proteins. Binding of a biomolecule to the surface of a microresonator will increase its path length, leading to a shift in the resonance frequency according to the reactive sensing principle. In this paper, we develop a theoretical expression that will link the reactive shift to the bacteria and microdisk parameters and help quantify the number of bacteria that bind to the surface of a 200μm-diameter silica microdisk.

Real-time label-free detection and kinetic analysis of Etanercept—Protein A interactions using quartz crystal microbalance

A quartz crystal microbalance (QCM) was constructed to assess if such a biosensor has value as a complementary real-time label-free analysis platform for the biopharmaceutical industry. This was achieved through modifying QCM crystals with a low-fouling carboxymethyl-dextran layer bearing Protein A, and then injecting solutions containing Etanercept (i.e., Enbrel®) into the QCM chambers. The kinetics of Enbrel® – Protein A interactions was modeled using the Langmuir binding model and Enbrel® concentrations between 0.75–300ngmL−1. The resulting equilibrium dissociation and association constants (KD and KA) were 5.06×10−8M and 1.98×107M−1, respectively. The association and dissociation rate constants (kon and koff) decreased substantially as Enbrel® concentration, [C], increased, despite that the net binding rate, (kon[C]+koff), increased. The decrease in kon and koff was hypothesized to be a consequence of mass transport limitations. To verify this, QCM dissipation measurements were analyzed to provide insight on solution viscosity. As Enbrel® concentration increased, the net change in dissipation, ΔD, became larger. An augmentation of ΔD is associated with a higher solution viscosity, which would result in an increase in mass transport limitations. Therefore, the decrease in kon and koff for increasing Enbrel® concentration can be attributed to mass transport limitations. In conclusion, QCM is a valuable complementary real-time label-free biosensor analysis platform for the biopharmaceutical industry. Unlike the surface plasmon resonance (SPR) platform, QCM allows measuring dissipation, which can provide insight on how mass transport limitations impact interaction kinetics.

Adsorption-Induced Surface Effects on the Dynamical Characteristics of Micromechanical Resonant Sensors for In Situ Real-Time Detection

By incorporating modified Langmuir kinetic model, a novel slowly time-varying dynamical model of in situ micromechanical sensors is proposed to real-time monitor atomic or molecular adsorptions on the solid surface in a viscous fluid. First, Langmuir kinetic model is modified by the introduction of time-varying concentrations of analytes. Second, van der Waals (vdW), Coulomb, and biomolecular interactions for uncharged adsorbates, charged ones, and double-stranded DNAs (dsDNAs) are adopted, respectively, to develop the governing equation of time-varying vibrational systems with Hamilton's principle. It can be found that the adsorption-induced surface effects are incorporated into the dynamical equation of sensors due to real-time adsorptions. Third, the dynamical model is validated with the theoretical results of O atoms on Si (100) surface and the experimental data of dsDNAs interactions. The results show that the dynamical behavior is adsorption-induced slowly time-varying vibration due to the time-varying effective mass, stiffness, damping, and equilibrium positions of the microcantilevers. Moreover, comparing the modified Langmuir kinetic model with the unmodified model, the amplitude and phase hysteresis phenomena of frequency shift for resonant sensors can result in huge detection errors. In addition, the fluid effect can dramatically degrade the sensitivity and precision of real-time detection by several orders, which can provide a theoretical foundation to improve the detection sensitivity by reducing the fluid effect. The work demonstrates that it is essential to develop a time-varying dynamical model for in situ real-time label-free detection technique.

Real-Time Detection of Staphylococcus Aureus Using Whispering Gallery Mode Optical Microdisks.

Whispering Gallery Mode (WGM) microresonators have recently been studied as a means to achieve real-time label-free detection of biological targets such as virus particles, specific DNA sequences, or proteins. Due to their high quality (Q) factors, WGM resonators can be highly sensitive. A biosensor also needs to be selective, requiring proper functionalization of its surface with the appropriate ligand that will attach the biomolecule of interest. In this paper, WGM microdisks are used as biosensors for detection of Staphylococcus aureus. The microdisks are functionalized with LysK, a phage protein specific for staphylococci at the genus level. A binding event on the surface shifts the resonance peak of the microdisk resonator towards longer wavelengths. This reactive shift can be used to estimate the surface density of bacteria that bind to the surface of the resonator. The limit of detection of a microdisk with a Q-factor around 104 is on the order of 5 pg/mL, corresponding to 20 cells. No binding of Escherichia coli to the resonators is seen, supporting the specificity of the functionalization scheme.

Label-free biosensor using nanogap embedded dielectric modulated schottky tunneling source impact ionization MOS

In this paper, we have investigated a novel nanogap embedded dielectric modulated schottky tunneling source impact-ionization MOS (DM-STS-IMOS) for highly sensitive, real-time label-free electrical detection of bio-molecules. The current gating mechanism of STS-IMOS is governed by cumulative effect of both impact ionization and source induced tunneling. Both of these mechanisms are synergistically leveraged for pathogenic biomolecule sensors design scheme. Technology computer-aided design (TCAD) simulation study is deployed to provide physical insight into the working mechanism and performance estimation of the proposed sensor. DM-STS-IMOS exhibits enhanced sensitivity and as the operating voltage of DM-STS-IMOS is lower than the conventional IMOS, it has significantly enhanced reliability and higher power efficiency. The length of the nanogap is recognized as a potential parameter to optimize the device sensitivity. It demonstrates dominant dielectric modulation effects, easy recovery mechanism and higher sensitivity even at smaller channel lengths. It can also be exploited in array-based screening and in-vivo bio-species diagnostics.

Dielectrophoresis-Enhanced Plasmonic Sensing with Gold Nanohole Arrays

We experimentally demonstrate dielectrophoretic concentration of biological analytes on the surface of a gold nanohole array, which concurrently acts as a nanoplasmonic sensor and gradient force generator. The combination of nanohole-enhanced dielectrophoresis, electroosmosis, and extraordinary optical transmission through the periodic gold nanohole array enables real-time label-free detection of analyte molecules in a 5 μL droplet using concentrations as low as 1 pM within a few minutes, which is more than 1000 times faster than purely diffusion-based binding. The nanohole-based optofluidic platform demonstrated here is straightforward to construct, applicable to both charged and neutral molecules, and performs a novel function that cannot be accomplished using conventional surface plasmon resonance sensors.

Real-time label-free detection of dividing cells by means of lensfree video-microscopy

Quantification of cell proliferation and monitoring its kinetics are essential in fields of research such as developmental biology, oncology, etc. Although several proliferation assays exist, monitoring cell proliferation kinetics remains challenging. We present a novel cell proliferation assay based on real-time monitoring of cell culture inside a standard incubator using a lensfree video-microscope, combined with automated detection of single cell divisions over a population of several thousand cells. Since the method is based on direct visualization of dividing cells, it is label-free, continuous, and not sample destructive. Kinetics of cell proliferation can be monitored from a few hours to several days. We compare our method to a standard assay, the EdU proliferation assay, and as proof of principle, we demonstrate concentration-dependent and time-dependent effect of actinomycin D-a cell proliferation inhibitor.