High sensitivity refractive index sensor based on micro-fiber with micro-arched transition

We demonstrated modulation of the waveguide mode mismatch via liquid cladding of the controllable refractive index for label-free quantitative detection of concentration of chemical or biological substances. A multimode optical fiber with its core exposed was used as the sensor head with the suitable chemical modification of its surface. Injected analyte liquid itself formed the liquid cladding for the waveguide. We found that modulation of the concentration of analyte injected enables a degree of the waveguide mode mismatch to be controlled, resulting in sensitive change in optical power transmission, which was utilized for its real-time quantitative assay. We applied the device to quantitating concentration of glycerol and bovine serum albumin (BSA) solutions. We obtained experimentally the limit of detection (LOD) of glycerol concentration, 0.001% (volume ratio), corresponding to the resolvable index resolution of ∼1.02 × 10-6 RIU (refractive index unit). The presented sensors also exhibited reasonably good reproducibility. In BSA detection, the sensor device response was sensitive to change in the refractive indices not only of liquid bulk but also of layers just above the sensing surface with higher sensitivity, providing the LOD experimentally as ∼3.7 ng/mL (mass coverage of ∼30 pg/mm2). A theoretical model was also presented to invoke both mode mismatch modulation and evanescent field absorption for understanding of the transmission change, offering a theoretical background for designing the sensor head structure for a given analyte. Interestingly, the device sensing length played little role in the important sensor characteristics such as sensitivity, unlike most of the waveguide-based sensors. This unraveled the possibility of realizing a highly simple structured label-free sensor for point-of-care testing in a real-time manner via an optical waveguide with liquid cladding. This required neither metal nor dielectric coating but still produced sensitivity comparable to those of other types of label-free sensors such as plasmonic fiber ones.

The osmotic pressure of concentrated protein solutions: Effect of concentration and ph in saline solutions of bovine serum albumin

A compact and high sensitivity refractive index (RI) sensor has been theoretically and experimentally demonstrated based on dual-mode interferometer (DMI) in an eccentric core few-mode fiber (ECFMF). The DMI is fabricated by fusion splicing a piece of ECFMF etched by hydrofluoric acid (HF) and two single mode fibers (SMFs) with a lateral-offset. The interference is formed by LP01 and LP11 modes in the eccentric core of ECFMF. The etched ECFMF-DMI based on core-core mode interference exhibits a higher RI sensitivity than the DMI based on core-cladding mode interference. The sensitivity reaches up to 2565.2 nm/RIU around the RI of 1.4. Both of the etched and unetched ECFMF-DMIs have low temperature sensitivities of 9.6 pm/°C and 33.1 pm/°C, respectively. The etched ECFMF-DMI based on the core-core mode interference possesses tremendous superiority for RI measurement due to its high RI sensitivity and low temperature cross, therefore the proposed sensor has great potentials in chemical and biological fields.

A compact and ultra high sensitive RI sensor using modal interference in an integrated optic waveguide with metal under-cladding

Concentrated Aqueous Protein Systems, Proton Relaxation Times, Slow Chemical Exchange In this paper we present proton spin-lattice (T1) and spin-spin (T2) relaxation times measured vs. concentration, temperature, pulse interval (tauCPMG) as well as 1H NMR spectral measurements in a wide range of concentrations of bovine serum albumin (BSA) solutions. The anomalous relaxation behaviour of the water protons, similar to that observed in mammalian lenses, was found in the two most concentrated solutions (44% and 46%). The functional dependence of the spin-spin relaxation time vs. tauCPMG pulse interval and the values of the motional activation parameters obtained from the temperature dependencies of spin-lattice relaxation times suggest that the water molecule mobility is reduced in these systems. The slow exchange process on the T2 time scale is proposed to explain the obtained data. The proton spectral measurements support the hypothesis of a slow exchange mechanism in the highest concentrated solutions. From the analysis of the shape of the proton spectra the mean exchange times between bound and bulk water proton groups (tauex) have been estimated for the range of the highest concentrations (30%-46%). The obtained values are of the order of milliseconds assuring that the slow exchange condition is fulfilled in the most concentrated samples.

Depressed index clad fiber as a highly sensitive low-cost refractive index sensor

There is a need for a new sensing device; one that is capable of sensing much lower concentrations at much faster rates than what is currently available. When these needs are satisfied, the new technology has the potential to improve healthcare by increasing the likelihood of early disease detection, reduce industrial manufacturing costs by increasing the speed to analyte measurement, and protect the people of the world in ways that are currently not possible by multiplexed testing capability to detect analytes such as poisons. There have been several technologies that have been developed to detect ultra-low analyte concentrations; however none of them are yet commercially viable. Silicon nanowires have the ability to satisfy the new sensing needs, while remaining commercially viable with a manufacturing process that could allow for mass production much easier than that of other technologies. Both modeling and experimentation was performed for this dissertation to enhance the knowledge of the functionality, sensitivity, and fabrication of silicon nanowire biosensors. Applying the results from this work, the design of the silicon nanowire chip enhanced the resolution of the sensor to detect pico-molar concentrations of Bovine Serum Albumin in solution with a 100 nA current signal change, and the fabrication studies have increased the functional device yield from 75% to 95%. Utilizing the electrodeposition methods for selectively coating the silicon nanowires and the easily scalable fabrication process developed through this endeavor will allow for ease of integration into a mass production environment, ultimately moving the viability of the technology commercialization forward.

Catalytic currents of albumin at the hanging mercury drop electrode

Relationship between SH group reactivity and concentration of bovine serum albumin and rat plasma

Ternary phase diagrams (TPDs) for aqueous bovine serum albumin (BSA) solutions containing ethanol or (NH4)2SO4 were determined for temperatures ranging from 20 to 70 degrees C. At 20 degrees C, ethanol destabilized BSA, resulting in gel formation at moderate solute concentrations. In contrast, (NH4)2SO4 concentrations above 20 wt % precipitated BSA from solution. Raising the temperature led to gel formation at increasingly lower BSA and solute concentrations. The removal of adsorbed fatty acids from BSA had little effect on the ethanol TPDs but reduced protein solubility in (NH4)2SO4. Moreover, the salt TPDs of fatty-acid-poor BSA were similar to those previously observed with S-ovalbumin.

Objective: The objective was to study the effect of concentrations of doxorubicin hydrochloride (Dox) and bovine serum albumin (BSA) in a sample on fluorescence intensity, UV absorbance, refractive index and optical rotation.Methods: A circumscribed central composite statistical design with 2 factors, 5 levels, and 13 runs was selected for the study. According to that influence of both in interaction was measured by fluorescence intensity, UV absorbance, refractive index and optical rotation and were analyzed by the design expert software.Results: It was observed that concentration of BSA alone was significantly affecting the fluorescence intensity and optical rotation of samples. Dox alone was having a significant effect on UV absorbance at 280 nm. In the case of a refractive index, both Dox and BSA were having a significant effect. But the effect of BSA was much pronounced than that of Dox on refractive index.Conclusion: Interaction studies between BSA and Dox would be beneficial as they are commonly used in combination with tumor-targeted delivery. The interaction was observed that in a linear model for a wide range of concentration of both. So it will be useful to determine the interaction of unknown concentration.

A high sensitive refractive index sensor based on the cladding etched photonic crystal fiber (PCF) Mach-Zehnder interferometer (MZI) is proposed, which is spliced a section of photonic crystal fiber between two single modes fibers (SMFs).The interference fringe of the MZI shifts with the variation of the ambient refractive index (RI). It is found that the RI sensitivity slightly decrease with an increase in the interference length. The sensitivities of MZI with 35 mm PCF, 40 mm PCF, and 45 mm PCF are 106.19 nm/RIU, 93.33 nm/RIU, and 73.64 nm/RIU, respectively, in the range of 1.333 to 1.381. After etched, the RI sensitivity of the MZI could be improved obviously. The RI sensitivities of the MZI with 35 mm PCF are up to 211.53 nm/RIU and 359.37 nm/RIU when the cladding diameter decreases to 112 μm and 91 μm, respectively. Moreover, the sensor is insensitive to temperature, and the measured sensitivity is only 9.21 pm/°C with the range from 20°C to 500°C. In addition, the sensor has advantage of simple fabrication, low cost, and high RI sensitivity.

Plasmonic nanostructures with strong on-resonance local electric fields at the metal interfaces provide an excellent means for sensing applications. However, most plasmonic resonances suffer from relatively broad bandwidths, mainly due to the intrinsic material dissipation, restricting the optical performances. Moreover, little attention is paid on the radiation loss. In this work, we utilize quasi-guided modes supported by a metallic disk array and demonstrate the manipulation of radiation losses to further improve the resonance property. When a relative angle is introduced between every two adjacent metallic disks in a subwavelength-period array to form a zigzag metasurface, the period doubles leading to a transition of the true guided modes to be flipped above the light cone into the quasi-guided modes with finite yet relatively high-quality factors. We demonstrate the application of these quasi-guided modes with reduced bandwidths as refractive index sensors. Our experiment demonstrates that a refractive index sensitivity as high as 655 nm/RIU can be achieved with this structure, which has a good agreement with the numerical results. This sensitivity outperforms many other plasmonic sensors, e.g., those based on localized surface plasmon resonances or detuned plasmonic resonators. The proposed scheme of using quasi-guided modes as the refractive index sensor provides a prospective platform for biological and chemical sensing.

A high-sensitivity refractive index (RI) sensor based on the surface lattice resonance of periodic gold nanoparticle array is proposed. The influence of sensor structural parameters on the extinction spectrum is systematically investigated. The physical mechanism behind the extinction peak is discussed by the electric field simulations. The optimal structural parameters are determined by calculating and analyzing key sensing performance metrics, namely sensitivity and figure of merit (FOM). In the considered RI range, the optimal sensor exhibits a sensitivity of 562.42 nm RIU−1 and a FOM of 54.38 RIU−1. Notably, in a specific subrange, the sensitivity and FOM can reach maximum values of 600 nm RIU−1 and 60.61 RIU−1, respectively.

Formation of a carbonaceous film on the surface of Cu in a bovine serum albumin solution