Plasmonic photonic biosensor: in situ detection and quantification of SARS-CoV-2 particles.

We conceptualized and numerically investigated a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor for rapid detection and quantification of novel coronavirus. The plasmonic gold-based optical sensor permits three different ways to quantify the virus concentrations inside patient's body based on different ligand-analyte conjugate pairs. This photonic biosensor demonstrates viable detections of SARS-CoV-2 spike receptor-binding-domain (RBD), mutated viral single-stranded ribonucleic acid (RNA) and human monoclonal antibody immunoglobulin G (IgG). A marquise-shaped core is introduced to facilitate efficient light-tailoring. Analytes are dissolved in sterile phosphate buffered saline (PBS) and surfaced on the plasmonic metal layer for realizing detection. The 1-pyrene butyric acid n-hydroxy-succinimide ester is numerically used to immobilize the analytes on the sensing interface. Using the finite element method (FEM), the proposed sensor is studied critically and optimized for the refractive index (RI) range from 1.3348-1.3576, since the target analytes RIs fluctuate within this range depending on the severity of the viral infection. The polarization-dependent sensor exhibits dominant sensing attributes for x-polarized mode, where it shows the average wavelength sensitivities of 2,009 nm/RIU, 2,745 nm/RIU and 1,984 nm/RIU for analytes: spike RBD, extracted coronavirus RNA and antibody IgG, respectively. The corresponding median amplitude sensitivities are 135 RIU-1, 196 RIU-1 and 140 RIU-1, respectively. The maximum sensor resolution and figure of merit are found 2.53 × 10-5 RIU and 101 RIU-1, respectively for viral RNA detection. Also, a significant limit of detection (LOD) of 6.42 × 10-9 RIU2/nm is obtained. Considering modern bioassays, the proposed compact photonic sensor will be well-suited for rapid point-of-care COVID testing.

Plasmonic Micro-Channel Assisted Photonic Crystal Fiber Based Highly Sensitive Sensor for Multi-Analyte Detection.

A dual-channel propagation controlled photonic crystal fiber (PCF)-based plasmonic sensor was presented to detect multiple analytes simultaneously. Plasmonic micro-channels were placed on the outer surface of the PCF, which facilitates an easy sensing mechanism. The sensor was numerically investigated by the finite element method (FEM) with the perfectly matched layer (PML) boundary conditions. The proposed sensor performances were analyzed based on optimized sensor parameters, such as confinement loss, resonance coupling, resolution, sensitivity, and figure of merit (FOM). The proposed sensor showed a maximum wavelength sensitivity (WS) of 25,000 nm/refractive index unit (RIU) with a maximum sensor resolution (SR) of 4.0 × 10-6 RIU for channel 2 (Ch-2), and WS of 3000 nm/RIU with SR of 3.33 × 10-5 RIU for channel 1 (Ch-1). To the best of our knowledge, the proposed sensor exhibits the highest WS compared with the previously reported multi-analyte based PCF surface plasmon resonance (SPR) sensors. The proposed sensor could detect the unknown analytes within the refractive index (RI) range of 1.32 to 1.39 in the visible to near infrared region (550 to 1300 nm). In addition, the proposed sensor offers the maximum Figure of Merit (FOM) of 150 and 500 RIU-1 with the limit of detection (LOD) of 1.11 × 10-8 RIU2/nm and 1.6 × 10-10 RIU2/nm for Ch-1 and Ch-2, respectively. Due to its highly sensitive nature, the proposed multi-analyte PCF SPR sensor could be a prominent candidate in the field of biosensing to detect biomolecule interactions and chemical sensing.

Multi-Analyte Detection Based on Integrated Internal and External Sensing Approach.

Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light- guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10 -6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

Asymmetric core-guided polarization-dependent plasmonic biosensor.

A modified solid-core photonic crystal fiber (PCF)-based plasmonic sensor is proposed where light propagation through the PCF is controlled by scaling down of air holes. The modified core facilitates the easy excitation of the plasmonic surface, resulting in improved sensor performance. The chemically stable gold is externally coated on the PCF surface, which helps to establish surface plasmon resonance phenomena. The response of the sensor is analyzed based on the numerical method, and the design parameters are optimized to enhance the sensing performance. The asymmetric fiber-core structure provides the polarization controllability and significantly suppresses the y-polarized response to achieve a dominant x-polarized response and additional functionalities. The sensor exhibits a maximum wavelength sensitivity of 11,000 nm/RIU (refractive index unit) and sensing resolution of 9.09×10-6 RIU in the x-polarized mode. Also, the sensor exhibits maximum amplitude sensitivity of 631RIU-1, and a good figure of merit is 157RIU-1. Furthermore, the sensor can detect the unknown analytes' refractive index (RI) in the sensing analyte RI range of 1.33 to 1.40, which will lead to finding the potential applications in biomolecules, organic chemicals, and environment monitoring.

Mode-multiplex plasmonic sensor for multi-analyte detection.

Highly sensitive mode-multiplex miniaturized sensors enable the detection and quantification of multiple biomolecules simultaneously through their real-time interactions. Here, we demonstrate a grapefruit photonic crystal fiber (PCF)-based mode-multiplex surface plasmon resonance (SPR) sensor that detects multiple analytes simultaneously. Three grapefruit-shaped air-holes are internally coated with plasmonic gold (Au) material, which allows them to act as mode-multiplex channels that detect three unknown analytes. The sensor performance was investigated using the finite element method (FEM), and the optimized fiber structure was fabricated with the standard stack-and-draw method. For the y-polarized mode, channels one and three showed the maximum wavelength sensitivities of 2000 and 18,000 nm/RIU (refractive index unit) at the analyte refractive indices of 1.34 and 1.41, respectively. On the other hand, channel two showed the maximum wavelength sensitivity of 3000 nm/RIU at the analyte refractive index (RI) of 1.36 for the x-polarized mode. To the best of our knowledge, this is the first demonstration of a mode-multiplex grapefruit PCF-based SPR sensor to simultaneously detect and quantify three different analytes. We anticipate that the proposed sensor will find potential applications in the detection of real-time biomolecular interactions and binding affinity.

Highly sensitive selectively coated photonic crystal fiber-based plasmonic sensor.

Highly sensitive and miniaturized sensors are highly desirable for real-time analyte/sample detection. In this Letter, we propose a highly sensitive plasmonic sensing scheme with the miniaturized photonic crystal fiber (PCF) attributes. A large cavity is introduced in the first ring of the PCFs for the efficient field excitation of the surface plasmon polariton mode and proficient infiltration of the sensing elements. Due to the irregular air-hole diameter in the first ring, the cavity exhibits the birefringence behavior which enhances the sensing performance. The novel plasmonic material gold has been used considering the chemical stability in an aqueous environment. The guiding properties and the effects of the sensing performance with different parameters have been investigated by the finite element method, and the proposed PCFs have been fabricated using the stack-and-draw fiber drawing method. The proposed sensor performance was investigated based on the wavelength and amplitude sensing techniques and shows the maximum sensitivities of 11,000 nm/RIU and 1,420 RIU-1, respectively. It also shows the maximum sensor resolutions of 9.1×10-6 and 7×10-6 RIU for the wavelength and amplitude sensing schemes, respectively, and the maximum figure of merits of 407. Furthermore, the proposed sensor is able to detect the analyte refractive indices in the range of 1.33-1.42; as a result, it will find the possible applications in the medical diagnostics, biomolecules, organic chemical, and chemical analyte detection.