In this work, a localized plasmon-based sensor is developed for para-cresol (p-cresol) - a water pollutant detection. A nonadiabatic $40~\mu \text{m}$ of tapered optical fiber (TOF) has been experimentally fabricated and computationally analyzed using beam propagation method. For optimization of sensor’s performance, two probes are proposed, where probe 1 is immobilized with gold nanoparticles (AuNPs) and probe 2 is immobilized with the AuNPs along with zinc oxide nanoparticles (ZnO-NPs). The synthesized metal nanomaterials were characterized by ultraviolet-visible spectrophotometer (UV–vis spectrophotometer) and transmission electron microscope (HR-TEM). The nanomaterials coating on the surface of the sensing probe were characterized by a scanning electron microscope (SEM). Thereafter, to increase the specificity of the sensor, the probes are functionalized with tyrosinase enzyme. Different solutions of p-cresol in the concentration range of $0~\mu \text{M}$ – $1000~\mu \text{M}$ are prepared in an artificial urine solution for sensing purposes. Different analytes such as uric acid, $\beta $ -cyclodextrin, L-alanine, and glycine are prepared for selectivity measurement. The linearity range, sensitivity, and limit of detection (LOD) of probe 1 are $0~\mu \text{M}$ – $700~\mu \text{M}$ , 7.2 nm/mM (accuracy 0.977), and $59.90~\mu \text{M}$ , respectively; and for probe 2 are $0~\mu \text{M}$ – $1000~\mu \text{M}$ , 5.6 nm/mM (accuracy 0.981), and $57.43~\mu \text{M}$ , respectively. Thus, the overall performance of probe 2 is quite better due to the inclusion of ZnO-NPs that increase the biocompatibility of sensor probe. The proposed sensor structure has potential applications in the food industry and clinical medicine.

Water Pollutants p-Cresol Detection Based on Au-ZnO Nanoparticles Modified Tapered Optical Fiber

This article presents the photonic crystal fiber (PCF) based surface plasmon resonance (SPR) biosensor for early detection of malaria disease in humans by measurement of the variation of red blood cells (RBCs). In the proposed PCF, two layers of air holes are arranged in a hexagonal lattice structure and a thin film of gold-coating is used over PCF for the occurrence of SPR phenomena. It occurs when surface plasmon polariton (SPP)-mode coupled with the core-mode during phase-matching conditions. Malaria infected RBCs samples are filled into the PCF, which have own refractive index (RI) that shift the SPR resonance wavelength during confinement loss measurement. The resonance wavelength of malaria-infected RBCs samples is different from their normal RBCs samples due to the difference in RI of infected and normal RBCs samples. The proposed work is helpful in the detection of different stages of malaria-infected RBCs such as ring phase, trophozoite phase and Schizont phase by measuring the shift in resonance wavelength. The calculated wavelength sensitivities of the proposed sensor for the ring phase, trophozoite phase and Schizont phase RBCs are 13714.29 nm/RIU, 9789.47 nm/RIU, and 8068.97 nm/RIU, respectively in x-polarized direction and 14285.71 nm/RIU, 10000 nm/RIU, and 8206.9 nm/RIU, respectively in y-polarized direction with the maximum detection limit of 0.029. The proposed PCF-based SPR biosensor is suitable for the early diagnosis of malaria disease due to its enhanced sensing performance (low detection limit and high sensitivity).

Gold-Immobilized Photonic Crystal Fiber-Based SPR Biosensor for Detection of Malaria Disease in Human Body

Etched multicore fiber sensor using copper oxide and gold nanoparticles decorated graphene oxide structure for cancer cells detection.

Gold nanoparticles have excellent optical and plasmon properties and have enormous research potential when they combine with different ligands. Functionalized gold nanoparticles are widely used in drug delivery, biological detection, sensors, and even clinical treatment. At present, with the rapid development of functionalized gold nanoparticles, we think it is necessary to sort out the recent research results. In this paper, the synthesis, characteristics, and biological applications of the three aspects are introduced. Firstly, the synthetic methods of functionalized gold nanoparticles are reviewed, and the improvement of the commonly used synthetic methods is summarized. Then, the catalytic properties, oxidation resistance, and chirality optical properties are summarized in detail. Finally, we summarize the research progress in the field of biology in recent years.

Functionalized Gold Nanoparticles: Synthesis, Properties and Biomedical Applications

Highly sensitive and selective sensor probe using glucose oxidase/gold nanoparticles/graphene oxide functionalized tapered optical fiber structure for detection of glucose

Accurate cholesterol level measurement plays an important role in the diagnosis of severe diseases such as cardiovascular diseases, hypertension, anemia, myxedemia, hyperthyroidism, coronary artery illness. Traditionally, electrochemical sensors have been employed to detect the cholesterol level. However, these sensors have limitations in terms of sensitivity and selectivity. In this paper, a localized surface plasmon resonance (LSPR) -based biosensor is demonstrated that accurately detects and measures the concentration of cholesterol. In the present study, a tapered optical fiber-based sensor probe is developed using gold nanoparticles (AuNPs) and cholesterol oxidase (ChOx) to increase the sensitivity and selectivity of the sensor. Synthesized AuNPs were characterized by UV-visible spectrophotometer, transmission electron microscope (TEM), and energy dispersive X-ray spectroscopy (EDS). Further, coating of AuNPs over fiber was confirmed by scanning electron microscope (SEM). The developed sensor demonstrates for a clinically important cholesterol range of 0 to 10 mM, and the limit of detection is found to be 53.1 nM.

LSPR-based cholesterol biosensor using a tapered optical fiber structure.

In this paper, a cholesterol biosensor is developed using a single-mode fiber (SMF) and a hollow core fiber (HCF) to detect and measure the cholesterol concentration in the human body. The sensitivity of an SMF-HCF structure (sensor probe) has been enhanced by the localized surface plasmon resonance (LSPR) technique using the gold nanoparticles (AuNPs) of 11± 0.5 nm particle size. Furthermore, sensor probe was functionalized with cholesterol oxidase (ChOx) enzyme to increase the selectivity of biosensor. The synthesis of AuNPs is confirmed by a UV-visible spectrophotometer, transmission electron microscope (TEM), and energy-dispersive X-ray spectroscopy (EDS). Furthermore, the coating of AuNPs over an optical fiber is verified by scanning electron microscope (SEM). The linearity range and detection limit of the proposed sensor are 50 nM– $1~\mu \text{M}$ and 25.5 nM, respectively. The selectivity of biosensor has been determined with the 10-mM concentration of different solutions of cholesterol, glucose, urea, ascorbic acid, L-cysteine, and galactose that are generally present in serum.

LSPR-Based Cholesterol Biosensor Using Hollow Core Fiber Structure

Diabetes mellitus is a common health issue in human beings. It is very important to develop a highly selective and sensitive biosensor for the detection of glucose concentration in the human body. The proposed sensor is based on localized surface plasmon resonance (LSPR) technique. An optical tapered fiber structure is used to develop the proposed sensor. Gold nanoparticles (AuNPs) are used to increase the sensitivity of the sensor probe. AuNPs of size ~ 10 nm is synthesized for this purpose. The characterization of AuNPs was performed with the UV-vis spectroscopy, transmission electron microscope (TEM), and scanning electron microscope (SEM). Further, glucose oxidase enzyme is used to increase the selectivity of the sensor. The selectivity of sensor is tested with different analytes such as cholesterol, urea, L-cysteine, ascorbic acid, and galactose that are generally found in the serum.

Development of Glucose Sensor Using Gold Nanoparticles and Glucose-Oxidase Functionalized Tapered Fiber Structure

A highly sensitive and selective optical fiber-based enzymatic biosensor has been proposed in the present study for detection of uric acid (UA) in human serum. The working mechanism of sensor depends on surface plasma property and localized surface plasmon resonance technique. For this purpose, a micro-ball fiber sensor probe of $350~\mu \text{m}$ diameter was fabricated using advanced fusion-splicer and coated with gold nanoparticles (AuNPs) and graphene oxide (GO) in order to enhance its sensitivity. UV-Visible spectrophotometer and high-resolution transmission electron microscope (HR-TEM) were used to characterize the AuNPs solution and GO aqueous dispersion. The absorbance spectrum of AuNPs and GO are recorded at 519 nm and 230 nm, respectively. The coating of AuNPs and GO over fiber surface were verified by using a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). Thereafter, sensor probe was functionalized with the specific enzyme i.e. uricase for the UA detection. The linearity response of uricase/GO/AuNPs-coated micro-ball optical fiber sensor is reported in the range of $10~\mu \text{M}$ –1 mM UA concentrations. The reflectance of sensor linearly decreases with the increasing UA concentrations. Sensitivity of the sensor is 2.1 %/mM with a good slope of linearity with detection limit of $65.60~\mu \text{M}$ . To test the accuracy of proposed sensor, UA concentration in serum samples have also tested by using proposed sensor and A5800 Automatic Biochemical Analyzer. The results of the developed sensor are consistent with the results of A5800 Automatic Biochemical Analyzer. Thus, proposed sensor can be successfully utilized for UA detection in human serum samples.

Xia Zhang

Papers

LSPR-based cholesterol biosensor using a tapered optical fiber structure.

LSPR-Based Cholesterol Biosensor Using Hollow Core Fiber Structure

Highly sensitive and selective sensor probe using glucose oxidase/gold nanoparticles/graphene oxide functionalized tapered optical fiber structure for detection of glucose

Development of Glucose Sensor Using Gold Nanoparticles and Glucose-Oxidase Functionalized Tapered Fiber Structure

Development of Uric Acid Biosensor Using Gold Nanoparticles and Graphene Oxide Functionalized Micro-Ball Fiber Sensor Probe