Biological Sensor Applications Research Articles

Ultra-Stretchable, Adhesive, Conductive, and Antifreezing Multinetwork Borate Ester-Based Hydrogel for Wearable Strain Sensor and VOC Absorption.

Hydrogels based on borate ester bonds exhibit remarkable tensile strength and self-healing ability, which make them a promising material for various biological research and strain sensor applications. However, in order to meet the practical application of hydrogel strain sensors, they must also show high conductivity, frost resistance, and proper adhesion, which is still a continuous challenge. Herein, a triple network hydrogel was prepared using poly(vinyl alcohol) (PVA) as the first network, ethylene imine polymer (PEI) as the second network, and poly(acrylamide-co-acrylic acid) copolymer (denoted as P(AM-Co-AA)) as the third network. 3-Carboxy-4-fluorophenylboronic acid (CFBS) was used as the cross-linking agent, glycerol (GL) was added to improve low-temperature resistance, and sodium chloride (NaCl) was incorporated to enhance electrical conductivity. The resulting PVA-CFBS@PEI@P(AM-Co-AA) triple network hydrogel exhibited impressive mechanical properties, including ultra tensile strength (4100%, 266.8 kPa), high toughness (6.5 MJ/m3), and low-temperature resistance (-60 °C). Additionally, it demonstrated high conductivity (σ = 1.83 mS/cm). The incorporation of CFBS endowed the hydrogel with excellent self-healing ability, while GL improved low-temperature resistance and strain sensing sensitivity (gauge factor (GF) = 2.8 (0-300%), GF = 5.6 (300-600%), GF = 8.7 (600-1000%)). The prepared hydrogel sensor can repetitively detect and differentiate between a wide range of human activities such as joint movements, frowning, and smiling. Additionally, the hydrogel demonstrated favorable mechanical properties at -20 °C (good adhesion, tensile strength: 1169.8%, 1.2 MPa; conductivity: 0.71 mS/cm, and strain sensing coefficient: GF = 1.3), making it suitable for applications in low-temperature environments. Furthermore, it also functions as an exceptional adsorbent, capable of selectively absorbing volatile organic compounds at high capacity (e.g., methanol: 1.80 g/g; acetone: 1.50 g/g).

All‐Printed Electrically Driven Lighting via Electrochemiluminescence

AbstractElectrochemiluminescence (ECL) has attracted significant attention as a promising light‐emitting technology owing to its simple configuration and solution processability. ECL has wide applications in biological and chemical sensors, lighting, and displays. ECL lighting devices are fabricated as sandwiched structures with a transparent electrode on top, which limits their widespread adoption. Intricate structures with high precision and customizable designs can be directly fabricated using 3D printing. However, 3D printing of ECL devices is challenging because of poor printability and structural integrity of ECL luminophore inks. Here, all‐printed electrically driven lighting is demonstrated using the direct ink writing method. The ECL reactive layer and electrodes are directly printed using a side‐by‐side electrode configuration. A 3D printable ECL ink is developed by incorporating silica nanoparticles as rheological modifiers to realize well‐defined patterns with high structural integrity. Graphene is introduced on Ag multilayer electrodes to embrace both the electrical conductivity and electrochemical stability for efficient ECL operation. This all‐printing approach allows the fabrication of ECL devices with complex designs, such as combs and spirals. Moreover, it facilitates seamless printing on various substrate materials, making this technology an asset in the fields of biology, chemistry, and electronics.

Moisture‐Insensitive Force Sensor Yarns and Fabrics to Monitor Biological Motion

AbstractTextile sensors are crucial unobtrusive devices attached to arbitrarily curved surfaces owing to their high flexibility and ease of processing in large areas with complex contours. However, issues regarding the reliability and stability of the output of textile sensors and their practical implementation persist. This study proposes sensor yarns comprising carbon‐coated multifibers covering metallic core yarns to detect pressure and strain. Two electrically independent metallic core fibers are twisted in close proximity in a core‐sheath structure with a sheath yarn of carbon‐coated fibers. When an external force is applied, the covering yarns deform elastically, causing a change in resistance. The proposed sensor yarns can be used to develop customized textile sensors, as they can be woven or knitted at the target positions owing to their flexibility. Fabrics and knits with embedded sensor yarns can detect external forces and biological motions, e.g., respiratory monitoring and finger movements. The proposed sensors can be made sensitive or insensitive to moisture depending on the choice of the covering yarn. Thus, the proposed yarns and textile sensors have potential applications in wearable devices and biological sensors that require high conformability to the human body and curved surfaces.

STARCH BASED MICROSPHERE BIOLASERS

Recently, biolasers whose optical cavity is made of natural materials such as serum-extracted protein, egg white, cellulose, and gelatin have attracted a lot of attention. The advantage of these lasers is their biocompatibility and biodegradability which is significant for biointegration. In this study, we demonstrate that starch is a low-cost and good material for microsphere biolasers. By using a simple emulsion method with a dehydration process, dye-doped starch microsphere lasers with diameters ranging from 40 to 180 μm have been successfully obtained. Lasing properties are investigated and the results show that the lasing threshold is approximately 1.0 μJ and the quality factor can reach 2700. The starch-based microsphere lasers indicate excellent stability after a storage time of a month; thus, they are promising for practical applications in biological and chemical sensors.

Excitation of multiple Fano resonances on all-dielectric nanoparticle arrays.

In this paper, an all-dielectric metasurface consisting of a unit cell containing a nanocube array and organized periodically on a silicon dioxide substrate is designed and analyzed. By introducing asymmetric parameters that can excite the quasi-bound states in the continuum, three Fano resonances with high Q-factor and high modulation depth may be produced in the near-infrared range. Three Fano resonance peaks are excited by magnetic dipole and toroidal dipole, respectively, in conjunction with the distributive features of electromagnetism. The simulation results indicate that the discussed structure can be utilized as a refractive index sensor with a sensitivity of around 434 nm/RIU, a maximum Q factor of 3327, and a modulation depth equal to 100%. The proposed structure has been designed and experimentally investigated, and its maximum sensitivity is 227 nm/RIU. At the same time, the modulation depth of the resonance peak at λ = 1185.81 nm is nearly 100% when the polarization angle of the incident light is 0 °. Therefore, the suggested metasurface has applications in optical switches, nonlinear optics, and biological sensors.

Ultrasensitive Nanophotonic Random Spectrometer with Microfluidic Channels as a Sensor for Biological Applications.

Spectrometers are widely used tools in chemical and biological sensing, material analysis, and light source characterization. However, an important characteristic of traditional spectrometers for biomedical applications is stable operation. It can be achieved due to high fabrication control during the development and stabilization of temperature and polarization of optical radiation during measurements. Temperature and polarization stabilization can be achieved through on-chip technology, and in turn robustness against fabrication imperfections through sensor design. Here, for the first time, we introduce a robust sensor based on a combination of nanophotonic random spectrometer and microfluidics (NRSM) for determining ultra-low concentrations of analyte in a solution. In order to study the sensor, we measure and analyze the spectra of different isopropanol solutions of known refractive indexes. Simple correlation analysis shows that the measured spectra shift with a tiny variation of the ambient liquid optical properties reaches a sensitivity of approximately 61.8 ± 2.3 nm/RIU. Robustness against fabrication imperfections leads to great scalability on a chip and the ability to operate in a huge spectral range from VIS to mid-IR. NRSM optical sensors are very promising for fast and efficient functionalization in the field of selective capture fluorescence-free oncological disease for liquid/gas biopsy in on-chip theranostics applications.

A review on DNA/BSA binding and cytotoxic properties of multinuclear Schiff’s base complexes

Metallo-organic compounds play a significant role in pharmaceutical sciences for their multiple biological functions. Schiff base ligands, the versatile pharmacophores, have although been known since 1864, there is still burgeoning interest in their coordination compounds. These compounds have grabbed the attention of bioinorganic chemists worldwide for their ease of preparation, tendency to form highly stable complexes, exceptional biological roles, catalytic and sensor applications. The focus of this review is on recent developments in the design of homo/hetero-bimetallic complexes with Schiff base ligands narrowed down to investigations on DNA/BSA (Deoxyribonucleic acid and bovine serum albumin) binding abilities and cytotoxic activity relevant to anticancer studies. As metal ions are electron deficient, they have a natural tendency to interact with electron-rich biological molecules such as proteins and DNA. On binding, it initiates a cascade of events involving several biochemical cell reactions and associated signaling pathways having implications for cancer treatment. Bimetallic compounds are advantageous over monometallic counterparts due to their favorable physicochemical properties attributed to the cooperative effects between metal centers. In addition, higher binding efficiency, higher specificity for cancer cells, and better binding interactions with the DNA of cancer cells are other characteristic effects. This review provides an updated overview and perspectives on the strategies that have been adopted for the design of novel metal-based anticancer drugs.

Voltage-modulated surface plasmon resonance biosensors integrated with gold nanohole arrays.

Surface plasmon resonance (SPR) has emerged as one of the most efficient and attractive techniques for optical sensors in biological applications. The traditional approach of an EC (electrochemical)-SPR biosensor to generate SPR is by adopting a prism underneath the sensing substrate, and an angular scan is performed to characterize the reflectivity of target analytes. In this paper, we designed and investigated a novel optical biosensor based on a hybrid plasmonic and electrochemical phenomenon. The SPR was generated from a thin layer of gold nanohole array on a glass substrate. Using C-Reactive Protein (CRP) as the target analyte, we tested our device for different concentrations and observed the optical response under various voltage bias conditions. We observed that SPR response is concentration-dependent and can be modulated by varying DC voltages or AC bias frequencies. For CRP concentrations ranging from 1 to 1000 µg/mL, at the applied voltage of -600 mV, we obtained a limit of detection for this device of 16.5 ng/mL at the resonance peak wavelength of 690 nm. The phenomenon is due to spatial re-distribution of electron concentration at the metal-solution interface. The results suggest that CRP concentration can be determined from the SPR peak wavelength shift by scanning the voltages. The proposed new sensor structure is permissible for various future optoelectronic integration for plasmonic and electrochemical sensing.

Numerical Study of Surface Plasmon Resonance Biosensor Using Aluminium Oxide and Bismuth Telluride Nanomaterials for Skin Cancer Cell Detection

In the present article, a highly angular sensitive surface plasmon resonance sensor has been studied for early detection of skin cancer cell. The device’s basic design is based on the Kretschmann configuration, which uses an angular interrogation technique. The surface plasmon resonance biosensor has a high potential for detecting skin cancer cells. The variation of refractive index has been taken 1.35–1.38 for basal cell cancer (skin cancer). The proposed device has been stacked with multilayers having silver metal, CaF2 prism, Al2O3, and Bi2Te3 layers. In this article detection accuracy, angular sensitivity, the distribution of electric field intensity and figure of merit as performance parameters have been reported. The optimized value of angular sensitivity is 257.33°RIU−1. Similarly, some other performance parameters like detection accuracy, penetration depth, quality factor and distribution of electric field intensity have also been evaluated and the values are 0.3143 deg−1, 80.8883 RIU−1, 4.82×105 V/m and 112 nm respectively. The numerical simulation has been evaluated by COMSOL multiphysics and MATLAB software. The proposed biosensor may have been used in biological and chemical sensor applications.

Multi‐Stimuli Responsive Thiazolothiazole Viologen‐Containing Poly(2‐Isopropyl‐2‐Oxazoline) and Its Multi‐Modal Thermochromism, Photochromism, Electrochromism, and Solvatofluorochromism Applications

AbstractSmart materials are highly desirable over the recent decade due to the growing demand on complicated nature. Smart materials with stable stimuli‐responsive properties are widely applied in sensors, smart windows, displays, and chemical valves, but they are relatively rare. Most of the current chromic materials are triggered by one or two external stimuli, and only a few multi‐stimuli responsive instances still suffer by their restricting functional states, such as solution or polymer. To address these challenges, researchers are focusing their efforts on developing a new generation of multi‐stimulus responsive chromic materials. In this article, our group has adopted a new strategy for the synthesis of the multi‐stimuli responsive single polymeric material, which can be useful for different applications (such as thermochromism, photochromism, electrochromism, and solvatofluorochromism). Thiazolothiazole viologen (TTv)‐containing poly(2‐isopropyl‐2‐oxazoline) (PiPO) was synthesized using a one‐pot reaction where the living cationic polymer chains were reacted with thiazolothiazole viologen to produce multi‐stimuli responsive PiPO‐TTv. PiPO‐TTv‐based device demonstrated multi‐responsive properties due to the thermoresponsive properties of PiPO segments and photo‐, electro‐responsive properties of TTv monomer, respectively. PiPO‐TTv material, additionally exhibits fluorescence characteristics that makes it appealing for environmental and molecular biological sensor applications.

Square Shaped MEMS Capacitive Pressure Sensors for Biological Applications

The focus of this study is on mathematical modelling analysis and simulation of a micromechanical system based on a capacitive pressure sensor with a square diaphragm of 500 μm × 500 μm. The mechanical operation of the suggested device under the impact of a uniform pressure range employing different materials on the same arrangement is the subject of this research. The principle, design and comparative analysis of several MEMS materials are covered in this work. The deflection of the capacitive pressure sensor of roughly 0.285 μm and 30.36 pF, as well as the change in the capacitance value, are used to evaluate the device's performance. At a maximum pressure of 20 kPa at room temperature, the sensor's sensitivity is 56.24× 10-6 pF/pa, and the sensor’s response time is also reduced under static and dynamic loading circumstances. It can be seen that graphene materials have linear, stable, and repeatable properties when subjected to a uniform pressure range.

Control of Surface Plasmon Resonance in Silver Nanocubes by CEP-Locked Laser Pulse

Localized surface plasmon resonance (LSPR) of metal nanoparticles has attracted increasing attention in surface-enhanced Raman scattering, chemical and biological sensing applications. In this article, we calculate the optical extinction spectra of a silver nanocube driven by an ultrashort carrier envelope phase (CEP)-locked laser pulse. Five LSPR modes are clearly excited in the optical spectra. We analyze the physical origin of each mode from the charge distribution on different parts of the cubic particle and the dipole and quadrupole excitation features at the LSPR peaks. The charge distribution follows a simple rule that when the charge concentrates from the face to the corners of the cubic particle, the resonant wavelength red-shifts. Then we modulate the LSPR spectra by changing CEP. The results show that CEP has selective plasmon mode excitation functionality and can act as a novel modulation role on LSPR modes. Our work suggests a novel means to regulate LSPR modes and the corresponding optical properties of metal nanoparticles via various freedoms of controlled optical field, which can be useful for optimized applications in chemical and biological sensors, single molecule detection, and so on.

Metal-free and flexible surface-enhanced Raman scattering substrate based on oxidized carbon cloth

Flexible surface-enhanced Raman scattering (SERS) substrates show great potential application in environmental, biological and technological sensors. However, most of flexible SERS substrates are designed based on depositing or embedding metal (Ag, Au, Cu) particles on or into polymer supports or woven fibers without SERS activity, which suffer from complex manipulation processes and high cost. In this work, oxidized carbon cloth fabricated by chemical oxidation of commercial carbon cloth used as a metal-free and highly flexible SERS substrate with detection of limit for Rhodamine 6G down to below 10−8 M is reported. The SERS sensitivity of oxidized carbon cloth is improved by more than 3 order magnitude than untreated carbon cloth. By combining experimental analyses and theoretical calculations, it is proved that rich oxygen-containing functional groups on carbon cloth surface introduced by chemical oxidation leads to enhanced charge transfer (chemical enhancement) between oxidized carbon cloth and adsorbed molecules, which is responsible for the improved SERS performance. This work may pave the way for metal-free and flexible SERS substrate design and provides valuable insights for carbon-based SERS substrate.

Mxene-Ceria Nanocomposite for Health Monitoring Sensorssa

MXenes are an emerging class of 2D layered nanomaterials that provide large surface area, hydrophilicity, high ion transport properties, low diffusion barrier, biocompatibility, and ease of surface functionalization. Due to their unique features, MXenes have gained substantial attention in fields such as batteries and supercapacitors and their application in chemical and biological sensors is growing. Their composition and layered structure make MXenes particularly attractive for biosensing applications. This presentation is focused on the synthesis and characterization of MXene-CeO2 nanocomposite for glucose sensing. The developed MXene-nanoparticles hybrid was then used as a transducer surface and supporting material for the immobilization of enzymes in an electrochemical biosensor setup. The incorporation of MXene into the sensor design enhanced the efficiency of the developed biosensor in terms of facilitating charge transfer and maximizing cerium oxide and biomolecule loading. Opportunities for developing wearable sensors and systems with integrated biomolecule recognition will be highlighted.

Extremely intense green up-conversion luminescent and ultra-high temperature sensitivity in Er3+/Yb3+ co-doped BiTa7O19 phosphors

Er3+/Yb3+ co-doped BiTa7O19 phosphors with bright pure green emission were synthesized first by a solid-state reaction method. The lattice structure and morphology of the synthesized samples was determined by X-ray diffraction (XRD) and field emission scan electronic microscope (FESEM). These samples’ up-conversion luminescence (UCL) and optical temperature sensing behavior were investigated by photoluminescence spectroscopy under 980 nm laser diode (LD) excitation. The optimum values of Er3+ and Yb3+ doping concentration were 10 mol % and 40 mol %, respectively. Further optimizing the preparation process of (Bi0·5Er0.1Yb0.4)Ta7O19, the green UCL integrated intensity of (Bi0·5Er0.1Yb0.4)Ta7O19 is up to 1.32 times than that of commercial NaYF4: Er3+/Yb3+ phosphors under 980 nm LD 35.71 W/cm2 excitation. In addition, all Er3+/Yb3+ co-doped BiTa7O19 phosphors have a good green monochromaticity (Sgr), and the Sgr reached 0.98–0.99. Based on the fluorescence intensity ratio (FIR) of the transition emission of the thermally coupled 2H11/2 and 4S3/2 levels to the ground state, the maximum absolute sensitivity (SA) of optimized (Bi0·5Er0.1Yb0.4)Ta7O19 is calculated as high as 0.01624 K−1 at 475 K, which is much higher than other reported materials. These results indicate that BiTa7O19: Er3+/Yb3+ may have potential applications in biological imaging, fluorescent labels, and optical temperature sensors.

Organic Electrochemical Transistors: Ultrahigh‐Gain Organic Electrochemical Transistor Chemosensors Based on Self‐Curled Nanomembranes (Adv. Mater. 29/2021)

Achieving synergy between electrochemistry and microelectronics is a hard-hitting task. In article number 2101518, Carlos C. Bof Bufon and co-workers employ rolling-origami nanotechnology to build up novel organic electrochemical transistors (OECTs) featuring outstanding performance. The findings also anticipate that rolling-origami OECTs are enormously appealing candidates to future applications in chemical and biological sensors (viz., for neurotransmitter detection).

Hydrogel-Based Optical Ion Sensors: Principles and Challenges for Point-of-Care Testing and Environmental Monitoring.

Hydrogel is a unique family of biocompatible materials with growing applications in chemical and biological sensors. During the past few decades, various hydrogel-based optical ion sensors have been developed aiming at point-of-care testing and environmental monitoring. In this Perspective, we provide an overview of the research field including topics such as photonic crystals, DNAzyme cross-linked hydrogels, ionophore-based ion sensing hydrogels, and fluoroionophore-based optodes. As the different sensing principles are summarized, each strategy offers its advantages and limitations. In a nutshell, developing optical ion sensing hydrogels is still in the early stage with many opportunities lying ahead, especially with challenges in selectivity, assay time, detection limit, and usability.

Liquid Crystal Elastomers for Biological Applications

The term liquid crystal elastomer (LCE) describes a class of materials that combine the elastic entropy behaviour associated with conventional elastomers with the stimuli responsive properties of anisotropic liquid crystals. LCEs consequently exhibit attributes of both elastomers and liquid crystals, but additionally have unique properties not found in either. Recent developments in LCE synthesis, as well as the understanding of the behaviour of liquid crystal elastomers—namely their mechanical, optical and responsive properties—is of significant relevance to biology and biomedicine. LCEs are abundant in nature, highlighting the potential use of LCEs in biomimetics. Their exceptional tensile properties and biocompatibility have led to research exploring their applications in artificial tissue, biological sensors and cell scaffolds by exploiting their actuation and shock absorption properties. There has also been significant recent interest in using LCEs as a model for morphogenesis. This review provides an overview of some aspects of LCEs which are of relevance in different branches of biology and biomedicine, as well as discussing how recent LCE advances could impact future applications.

Strongly resonant silicon slot metasurfaces with symmetry-protected bound states in the continuum.

In this work, a novel all-dielectric metasurface made of arrayed circular slots etched in a silicon layer is proposed and theoretically investigated. The structure is designed to support both Mie-type multipolar resonances and symmetry-protected bound states in the continuum (BIC). Specifically, the metasurface consists of interrupted circular slots, following the paradigm of complementary split-ring resonators. This configuration allows both silicon-on-glass and free-standing metasurfaces and the arc length of the split-rings provides an extra tuning parameter. The nature of both BIC and non-BIC resonances supported by the metasurface is investigated by employing the Cartesian multipole decomposition technique. Thanks to the non-radiating nature of the quasi-BIC resonance, extremely high Q-factor responses are calculated, both by fitting the simulated transmittance spectra to an extended Fano model and by an eigenfrequency analysis. Furthermore, the effect of optical losses in silicon on quenching the achievable Q-factor values is discussed. The metasurface features a simple bulk geometry and sub-wavelength dimensions. This novel device, its high Q-factors, and strong energy confinement open new avenues of research on light-matter interactions in view of new applications in non-linear devices, biological sensors, and optical communications.

Design and Fabrication of a MEMS-Based Break Junction Device for Mechanical Strain-Correlated Optical Characterization of a Single-Molecule

Here, we propose a robust lab-on-a-chip system for multi-dimensional (electrical, optical, and mechanical) characterization of a single-molecule utilizing a Si micromachined micro-electromechanical-system (MEMS) chip. Our MEMS-based break junction (MEMS-BJ) utilizes conventional MEMS chip fabrication techniques to create an electrostatic comb actuator capable of trapping a single-molecule between two nanoscale metal electrodes with sub-nanometer displacement resolution. In order to achieve this functionality, components of the chip (e.g flexural spring, comb drive fingers) are delicately designed based on an analytical model and basic performance parameters are verified using a finite element analysis simulation and capacitive sensor measurements. Using this system, we are able to perform combined single-molecule Raman spectroscopy and molecular conductance measurements in real-time. Finally, we present a representative case study of the multi-dimensional characterization of a single-molecule junction by analyzing correlated electrical, optical, and mechanical information while mechanically modulating the strain on the junction which allows for direct observation of the interplay between molecular structure and electron transport. We believe that our MEMS-BJ system will enable a deeper multi-dimensional study at a single-molecule level promoting the development of new methods for chemical and biological sensor applications.