Marcin Koba

Recognition of bacterial lipopolysaccharide using bacteriophage-adhesin-coated long-period gratings

In this paper we present a new type of highly sensitive label-free sensor based on long-period gratings (LPG) coated with T4 bacteriophage (phage) adhesin. The adhesin (gp37) binds Escherichia coli B (E. coli B) by recognizing its bacterial lipopolysaccharide (LPS). The LPG biofunctionalization methodology is based on coating LPG surface with nickel ions capable of gp37 histidine tag reversible binding. For the first time recombinant adhesive phage protein has been used as a receptor molecule in biosensing scheme. The specificity of LPS binding by adhesin has been tested with LPG-based device and confirmed using Western blot, Enzyme-Linked Immunosorbent Assay (ELISA) and BIACORE methods. The LPG-based sensor can measure bacterial contamination in real time and with a high accuracy. We show that T4 phage adhesin binds E. coli B LPS in its native or denatured form. The binding is highly specific and irreversible. The applied procedure allows for obtaining reusable biosensors.

Label-free sensitivity of long-period gratings enhanced by atomic layer deposited TiO 2 nano-overlays

In this paper, we discuss an impact of thin titanium dioxide (TiO(2)) coatings on refractive index (RI) sensitivity and biofunctionalization of long-period gratings (LPGs). The TiO(2) overlays on the LPG surfaces have been obtained using atomic layer deposition (ALD) method. This method allows for a deposition of conformal, thickness-controlled, with well-defined optical properties, and high-RI thin films which are highly desired for optical fiber sensors. It has been found that for LPGs working at a dispersion turning point of higher order cladding modes only tens of nanometers of TiO(2) overlay thickness allow to obtain cladding mode transition effect, and thus significant improvement of RI sensitivity. When the TiO(2) overlay thickness reaches 70 nm, it is possible to obtain RI sensitivity exceeding 6200 nm/RIU in RI range where label-free sensors operate. Moreover, LPGs with TiO(2)-enhanced RI sensitivity have shown improved sensitivity to bacteria endotoxin (E. coli B lipopolysaccharide) detection, when TiO(2) surface is functionalized with endotoxin binding protein (adhesin) of T4 bacteriophage.

Measurements of reactive ion etching process effect using long-period fiber gratings

The paper presents for the first time a study of long-period fiber gratings (LPFGs) applied for the measurements of reactive ion etching (RIE) process effect in various places of a plasma reactor. For the purposes of the experiment a number of highly sensitive LPFGs working at the dispersion turning point was fabricated using electric arc discharges. We show that the LPFGs allow for monitoring of the phenomena taking place in the reactor, especially those resulting in reduction of the LPFG diameter. Results of the measurements supported by simulations have shown that etching rate significantly decreases with elevation of the sample up to 3.6 mm over the electrode in the reactor, and stays constant above this height.

Towards refractive index sensitivity of long-period gratings at level of tens of µm per refractive index unit: fiber cladding etching and nano-coating deposition

In this work we report experimental results on optimizing the refractive index (RI) sensitivity of long-period gratings (LPGs) by fiber cladding etching and thin aluminum oxide (Al2O3) overlay deposition. The presented LPG takes advantage of work in the dispersion turning point (DTP) regime as well as the mode transition (MT) effect for higher-order cladding modes (LP09 and LP010). The MT was obtained by depositing Al2O3 overlays with single-nanometer precision using the Atomic Layer Deposition method (ALD). Etching of both the overlay and the fiber cladding was performed using hydrofluoric acid (HF). For shallow etching of the cladding, i.e., DTP observed at next = 1.429 and 1.439 RIU for an LPG with no overlay, followed by deposition of an overlay of up to 167 nm in thickness, HF etching allowed for post-deposition fine-tuning of the overlay thickness resulting in a significant increase in RI sensitivity mainly at the DTP of the LP09 cladding mode. However, at an external RI (next) above 1.39 RIU, the DTP of LP010 was noticed, and its RI sensitivity exceeded 9,000 nm/RIU. Deeper etching of the cladding, i.e., DTP observed for next above 1.45 RIU, followed by the deposition of thicker overlays (up to 201 nm in thickness) allowed the sensitivity to reach values of over 40,000 nm/RIU in a narrow RI range. Sensitivity exceeding 20,000 nm/RIU was obtained in an RI range suitable for label-free biosensing applications.

Combined Plasma-Based Fiber Etching and Diamond-Like Carbon Nanooverlay Deposition for Enhancing Sensitivity of Long-Period Gratings

This paper presents an application of reactive ion etching followed by diamond-like carbon nanooverlay deposition using radio frequency plasma-enhanced chemical vapor deposition method for effective tuning of the refractive index (RI) sensitivity of long-period gratings (LPGs). Both etching and deposition take place within one process. Combination of both plasma-based processes allows for well-controlled tuning of the LPG sensorial response up to its operation at both dispersion turning point of higher order cladding modes and mode transition regime. As a result of the processing, the RI sensitivity has been enhanced up to over 12 000 nm/RIU per single resonance in narrow RI range (1.3344-1.3355 RIU) and over 2000 nm/RIU in broader RI range (1.34-1.356 RIU). Experimental results have been supported by numerical analyses that show capabilities for further significant improvement of both RI sensitivity and range of RI measured with the enhanced sensitivity.

Tuning properties of long-period gratings by plasma post-processing of their diamond-like carbon nano-overlays

This work presents an application of reactive ion etching (RIE) for effective tuning of spectral response and the refractive index (RI) sensitivity of diamond-like carbon (DLC) nano-coated long-period gratings (LPGs). When oxygen plasma is applied the technique allows for an efficient and well controlled etching of hard and chemically resistant DLC films deposited on optical fibers. We show that optical properties of DLC, especially its refractive index, strongly depend on thickness of the film when it is thinner than 150 nm. The effect of DLC nano-coating deposition and etching on spectral properties of the LPGs is discussed. We have correlated the DLC properties with the shift of the LPG resonance wavelength and have found that both deposition and etching processes took place less effectively than on the electrode when the LPG sample was held above the electrode in the plasma reactor. An advantage of plasma-based etching is a capability for post-processing of the nano-coated structures with a good precision, as well as cleaning the samples and their re-coating according to requested needs. Moreover, the application of RIE allows for post-fabrication tuning of RI sensitivity of the DLC nano-coated LPGs.

Approximate Analysis of Nonlinear Operation of Square Lattice Photonic Crystal Laser

In this paper, an approximate method for the analysis of 2-D square lattice photonic crystal laser operation above the threshold is presented. Our approach is based on coupled wave equations, including gain saturation effect, and energy theorem. An expression for the small signal gain coefficient as a function of the output power, losses, coupling strength depending on the shape of the primitive cell of photonic crystal as well as index contrast, and active medium dimension is derived. Laser characteristics obtained reveal optimal coupling strength, for given structure parameters, for which maximal power efficiency of the laser structure is obtained.

Bacteriophage Adhesin-Coated Long-Period Grating-Based Sensor: Bacteria Detection Specificity

In this paper, we study a label-free detection specificity of an optical fiber long-period grating (LPG) biosensor working near the dispersion turning point of higher order cladding modes. The LPG sensor is functionalized with bacteriophage adhesin and tested with specific and nonspecific bacteria dry weights. It is shown that that such a biosensor is able to selectively bind to specific bacterial strains. In the experiments bacteria dry weights of E. coli B were used as a positive test and E. coli K12 and Salmonella enterica as negative tests. The resonance wavelength shift induced by E. coli B reaches over 90 nm, while for E. coli K12 and Salmonella enterica approximately 40 and 20 nm, respectively. Additionally, whole-cell-ELISA tests were made to confirm LPG-based biosensor outcomes, and numerical simulations were conducted to estimate biolayer impact on sensors performance.

Label-free Gram-negative bacteria detection using bacteriophage-adhesin-coated long-period gratings.

This paper presents a novel application of a highly sensitive sensor based on long-period gratings (LPGs) coated with T4 bacteriophage adhesin for Gram-negative bacteria detection. We show here, that the sensor evidently recognizes Escherichia coli K-12 (PCM2560), whereas in the reference tests - ELISA and BIAcore - the results are questionable. For LPGs sensor the resonant wavelength shift observed for E. coli K-12 was approximately half of that measured for E.coli B (positive control). The BIAcore readings (RU) for E. coli K-12 were at 10% level of the signal obtained for E .coli B. These results confirm the improved sensitivity of the LPGs sensor. Moreover, we also show that application of adhesin may allow for efficient detection of E. coli O111 (PCM418), Klebsiella pneumoniae O1 (PCM1) and Yersinia enterocolitica O1 (PCM1879). The specificity of binding bacteria by the adhesin is discussed and it is determined by a distinct region of lipopolysaccharide receptors and/or by the presence of outer-membrane protein C in an outer membrane of Gram-negative bacteria.

Nonlinear Operation of a 2-D Triangular Lattice Photonic Crystal Laser

In this paper, an approximate method is presented for the analysis of 2-D triangular lattice photonic crystal laser operation above the threshold. Our approach is based on coupled wave equations, including gain saturation and spatial hole burning effects, and energy theorem. An expression is derived for the small signal gain coefficient for transverse magnetic modes as a function of the output power, losses, coupling strength depending on the shape of the primitive cell of a photonic crystal as well as the index contrast. The laser characteristics obtained reveals optimal coupling strength, for given structure parameters, for which maximal power efficiency of the laser structure is obtained.