LSPR Sensor Chip Fabricated Based on Au Nanoparticles: Effect of Graphene Oxide and Reduced Graphene Oxide

Nanoparticles of noble metals are well known to display unique optical properties due to the localized surface plasmon resonance (LSPR) phenomenon, making them applicable for use as transducers in various LSPR sensor configurations. In order to develop a sensor chip, Au nanoparticles (AuNPs) were decorated onto a transparent glass substrate in the form of a uniform, high-density single layer using a self-assembly monolayer (SAM) process. The glass substrate surface was initially modified with amine functional groups using different concentrations of (3-Aminopropyl) triethoxysilane (APTES), followed by its optimization to reach a uniform monolayer of AuNPs. The optimized substrate was subsequently prepared by functionalization with APTES, while also being immersed into colloidal AuNPs. A uniform layer of Graphene oxide (GO) and reduced graphene oxide (rGO) sheets were coated on the AuNPs thin films using the dip-coating technique. The AuNPs/GO and rGO hybrid films were employed along with an appropriate optical set up acting as a smart sensor chip for detection of different concentrations of biomaterials. The optimum LSPR sensor (%0.5 APTES immersed in colloidal AuNPs for 12 h) resulted in a chip with %29 absorption and sharper plasmon peak. This appropriate condition remained constant after adding rGO, indicating that Glass/AuNPs/rGO chip will be suitable for sensory applications.

Pressure sensor chip utilizing electrical circuit of piezosensitive differential amplifier with negative feedback loop (PDA-NFL) for 5 kPa

High sensitive (S = 11.2 ± 1.8 mV/V/kPa with nonlinearity error 2KNL = 0.15 ± 0.09%/FS) small-sized (4.00x4.00 mm2) silicon pressure sensor chip utilizing new electrical circuit for microelectromechanical systems (MEMS) in the form of differential amplifier with negative feedback loop (PDA-NFL) for 5 kPa differential was developed. The advantages are demonstrated in the array of output characteristics, which prove the relevance of the presented development, relative to modern developments of pressure sensors with Wheatstone bridge electrical circuit for 5 kPa range.

Pressure Sensor with Novel Electrical Circuit Utilizing Bipolar Junction Transistor

<p>High sensitivity MEMS pressure sensor chip for different ranges (1 to 60 kPa) utilizing the novel electrical circuit of piezosensitive differential amplifier with negative feedback loop (PDA-NFL) is developed. Pressure sensor chip PDA-NFL utilizes two bipolar-junction transistors (BJT) with vertical n-p-n type structure (V-NPN) and eight piezoresistors (p-type). Both theoretical model of sensor response to pressure and temperature and experimental data are presented. Data confirms the applicability of theoretical model. Introduction of the amplifier allows for decreasing chip size while keeping the same sensitivity as a chip with classic Wheatstone bridge circuit.</p>

Pressure Sensor with New Electrical Circuit Utilizing Bipolar Junction Transistor

High sensitivity MEMS pressure sensor chip for different ranges (1 to 60 kPa) utilizing the novel electrical circuit of piezosensitive differential amplifier with negative feedback loop (PDA-NFL) is developed. Pressure sensor chip PDA-NFL utilizes two bipolar-junction transistors (BJT) with vertical n-p-n type structure (V-NPN) and eight piezoresistors (p–type). Both theoretical model of sensor response to pressure and temperature and experimental data are presented. Data confirms the applicability of theoretical model. Introduction of the amplifier allows for decreasing chip size while keeping the same sensitivity as a chip with classic Wheatstone bridge circuit.

Pressure Sensor with Novel Electrical Circuit Utilizing Bipolar Junction Transistor

<p>High sensitivity MEMS pressure sensor chip for different ranges (1 to 60 kPa) utilizing the novel electrical circuit of piezosensitive differential amplifier with negative feedback loop (PDA-NFL) is developed. Pressure sensor chip PDA-NFL utilizes two bipolar-junction transistors (BJT) with vertical n-p-n type structure (V-NPN) and eight piezoresistors (p-type). Both theoretical model of sensor response to pressure and temperature and experimental data are presented. Data confirms the applicability of theoretical model. Introduction of the amplifier allows for decreasing chip size while keeping the same sensitivity as a chip with classic Wheatstone bridge circuit.</p>

Pressure Sensor with New Electrical Circuit Utilizing Bipolar Junction Transistor

High sensitivity MEMS pressure sensor chip for different ranges (1 to 60 kPa) utilizing the novel electrical circuit of piezosensitive differential amplifier with negative feedback loop (PDA-NFL) is developed. Pressure sensor chip PDA-NFL utilizes two bipolar-junction transistors (BJT) with vertical n-p-n type structure (V-NPN) and eight piezoresistors (p-type). Both theoretical model of sensor response to pressure and temperature and experimental data are presented. Data confirms the applicability of theoretical model. Introduction of the amplifier allows for decreasing chip size while keeping the same sensitivity as a chip with classic Wheatstone bridge circuit.

Bimetallic structures to enhance the performance of surface plasmon resonance sensors

<p><b>Surface plasmon resonance (SPR) sensing is a label−free and rapid detection method and has extensive applications in the field of medical diagnostics, food control, and environmental monitoring. However, the lack of sensitivity to detect small molecules is a continuing concern in the application of this technique. Past research has explored different plasmonic structures such as metal nanoparticles, metallic nanoslits, nanoholes, colloidal Au nanoparticles, 2D nanomaterials, and multilayer structures as the sensing layer to improve the sensitivity of these sensors. However, the sensitivity improvement could be realised only with the cost of the increased complexity of optical configuration and sensor chip fabrication. Silver (Ag) is a very good candidate as the metallic layer for the sensor chip due to its higher electrical conductivity as compared to gold (Au). Besides cost−effectiveness, Ag thin film based sensors have better sensitivity with a sharp resonance dip and a high signal−to−noise ratio. However, the poor chemical stability of Ag thin films prevents their use in practical applications. Noble metals such as Au and platinum (Pt) offer greatly enhanced chemical stability. This work investigated the development of SPR sensors composed of a silver−noble metal bilayer structure to utilize both the sensitivity of silver and the chemical stability of the noble metal.</b></p> <p>To enable this research, an automated experimental SPR testbed for sensor characterisation was designed and constructed. This testbed is based on the Kretschmann configuration, using a He−Ne laser source at 632.8 nm. SPR sensor consisting of multilayer metal structures was fabricated using standard microelectronic fabrication techniques.</p> <p>The influence of the relative thickness of a noble metal capping layer on the SPR response and sensitivity from the Ag layer was systematically optimised, using both theoretical and experimental approaches. A theoretical analysis of the performance of the bimetallic SPR sensors was done using the transfer matrix method (TMM) by assuming a five−layer configuration. In the case of an Au capping layer, these simulations indicate an optimised thickness of 45 nm for Ag and 5 nm for Au. The observation from experimental analysis of different thickness combinations of Ag and Au matched the simulated results. However, the results of the stability studies exclude the practical use of 45 nm Ag/5 nm Au structures, as long−term degradation of the Ag layer occurs. A structure of 40 nm Ag/10nm Au was thus selected as the best composition for sensor applications. It is showed that sensors fabricated with this structure showed enhanced sensitivity compared to single−layer Au sensors, with a sensitivity 50% higher than that of the single−layer Au sensor. In the case of Ag/Pt structures, simulations indicated enhanced sensitivity from a 10 nm Ag/16 nm Pt structure. However, experimental measurements did not show any evidence for SPP excitation of Pt at the measured wavelength of 632.8 nm, making it unsuitable as a capping layer in our studies.</p> <p>The application of 40 nm Ag/10 nm Au bimetal layers as biosensors was done by the immobilization of thiol−terminated vitamin B12 aptamers on the Au sensor surface. However, the results were not reproducible, and more work on the binding kinetics of this aptamer will need to be performed to use this in a biosensor structure.</p>

Bimetallic structures to enhance the performance of surface plasmon resonance sensors

<p><b>Surface plasmon resonance (SPR) sensing is a label−free and rapid detection method and has extensive applications in the field of medical diagnostics, food control, and environmental monitoring. However, the lack of sensitivity to detect small molecules is a continuing concern in the application of this technique. Past research has explored different plasmonic structures such as metal nanoparticles, metallic nanoslits, nanoholes, colloidal Au nanoparticles, 2D nanomaterials, and multilayer structures as the sensing layer to improve the sensitivity of these sensors. However, the sensitivity improvement could be realised only with the cost of the increased complexity of optical configuration and sensor chip fabrication. Silver (Ag) is a very good candidate as the metallic layer for the sensor chip due to its higher electrical conductivity as compared to gold (Au). Besides cost−effectiveness, Ag thin film based sensors have better sensitivity with a sharp resonance dip and a high signal−to−noise ratio. However, the poor chemical stability of Ag thin films prevents their use in practical applications. Noble metals such as Au and platinum (Pt) offer greatly enhanced chemical stability. This work investigated the development of SPR sensors composed of a silver−noble metal bilayer structure to utilize both the sensitivity of silver and the chemical stability of the noble metal.</b></p> <p>To enable this research, an automated experimental SPR testbed for sensor characterisation was designed and constructed. This testbed is based on the Kretschmann configuration, using a He−Ne laser source at 632.8 nm. SPR sensor consisting of multilayer metal structures was fabricated using standard microelectronic fabrication techniques.</p> <p>The influence of the relative thickness of a noble metal capping layer on the SPR response and sensitivity from the Ag layer was systematically optimised, using both theoretical and experimental approaches. A theoretical analysis of the performance of the bimetallic SPR sensors was done using the transfer matrix method (TMM) by assuming a five−layer configuration. In the case of an Au capping layer, these simulations indicate an optimised thickness of 45 nm for Ag and 5 nm for Au. The observation from experimental analysis of different thickness combinations of Ag and Au matched the simulated results. However, the results of the stability studies exclude the practical use of 45 nm Ag/5 nm Au structures, as long−term degradation of the Ag layer occurs. A structure of 40 nm Ag/10nm Au was thus selected as the best composition for sensor applications. It is showed that sensors fabricated with this structure showed enhanced sensitivity compared to single−layer Au sensors, with a sensitivity 50% higher than that of the single−layer Au sensor. In the case of Ag/Pt structures, simulations indicated enhanced sensitivity from a 10 nm Ag/16 nm Pt structure. However, experimental measurements did not show any evidence for SPP excitation of Pt at the measured wavelength of 632.8 nm, making it unsuitable as a capping layer in our studies.</p> <p>The application of 40 nm Ag/10 nm Au bimetal layers as biosensors was done by the immobilization of thiol−terminated vitamin B12 aptamers on the Au sensor surface. However, the results were not reproducible, and more work on the binding kinetics of this aptamer will need to be performed to use this in a biosensor structure.</p>

Application of Tamm Plasmon Polaritons and Cavity Modes for Biosensing in the Combined Spectroscopic Ellipsometry and Quartz Crystal Microbalance Method

Low-cost 1D plasmonic photonic structures supporting Tamm plasmon polaritons and cavity modes were employed for optical signal enhancement, modifying the commercially available quartz crystal microbalance with dissipation (QCM-D) sensor chip in a combinatorial spectroscopic ellipsometry and quartz microbalance method. The Tamm plasmon optical state and cavity mode (CM) for the modified mQCM-D sample obtained sensitivity of ellipsometric parameters to RIU of ΨTPP = 126.78 RIU−1 and ΔTPP = 325 RIU−1, and ΨCM = 264 RIU−1 and ΔCM = 645 RIU‑1, respectively. This study shows that Tamm plasmon and cavity modes exhibit about 23 and 49 times better performance of ellipsometric parameters, respectively, for refractive index sensing than standard spectroscopic ellipsometry on a QCM-D sensor chip. It should be noted that for the optical biosensing signal readout, the sensitivity of Tamm plasmon polaritons and cavity modes are comparable with and higher than the standard QCM-D sensor chip. The different origin of Tamm plasmon polaritons (TPP) and cavity mode (CM) provides further advances and can determine whether the surface (TPP) or bulk process (CM) is dominating. The dispersion relation feature of TPP, namely the direct excitation without an additional coupler, allows the possibility to enhance the optical signal on the sensing surface. To the best of our knowledge, this is the first study and application of the TPP and CM in the combinatorial SE-QCM-D method for the enhanced readout of ellipsometric parameters.