A novel application of a highly sensitive biosensor based on long-period fiber gratings (LPFG) coated with microporous polyelectrolyte coating for Gram-negative bacteria detection was investigated. The uniform microporous coating with large surface area was fabricated with weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) via layer-by-layer (LbL) assembly, followed by a brief exposure to acidic aqueous solutions at pH=4. The diameter of the micropores could be adjusted in a wide range by thermal treatment and ionic etching. The effect of pore size and surface topography on bacteria adhesion was examinged. Optofluidic LPFG platform for real-time monitoring of the bacteria binding/ adhesion in a flowing condition was investigated by measuring the spectral shift in the resonance wavelength. The coated LPFG platform was further functionalized with covalently immobilized bacteria antibody for specific bacterial detection with a concentration as low as 104 CFU/ml. Comparing with the widely used biosensors based on surface plasmon resonance (SPR), no moving part or metal deposition is required in our biosensor, making it highly sensitive, accurate, compact and cost effective.
Manganese is an important heavy metal element that influences nervous system. Detection of manganese in various mediums has thus attracted lots of attentions. Here we report a study on silver nanoparticles functionalized long-period fiber grating (LPFG) for manganese sensing. Silver nanoparticles (AgNPs) with a size in the range of 70nm10nm were synthesized with polyvinyl pyrrolidone (PVP)-glycol. The interplay between arginine, an agent that can cause aggregation of AgNPs, and Mn2+ leads to refractive index change in the AgNPs colloidal solution, thus a shift in the resonance wavelength of LPFG that is surrounded by the colloidal solution. A sensitivity of 0.2nm shift/10-6M was achieved using such strategy. We believe the integration of nanoparticles with LPFG represents a promising sensing strategy for more advanced applications important for not only environmental but also health science.
Rapid, accurate, and real-time measurements of ocean salinity are of great importance for a host of scientific, commercial and defense applications. We demonstrate a highly sensitive, fast-responding fiber-optic salinity sensor that integrates long-period fiber gratings (LPFG) with ionic strength-responsive hydrogel. Submicron-thick hydrogels were synthesized via layer-by-layer (LbL) assembly of partially quaternized poly(4-vinyl pyridine) (qP4VP) and poly(acrylic acid) (PAA), followed by chemical crosslinking of qP4VP and removal of PAA. Spectroscopic ellipsometry studies of hydrogels with 37% quaternized qP4VP revealed robust and reversible swelling/deswelling behavior of the coatings in solutions with different salt concentrations at pH 7.5. The performance of hydrogel-coated LPFG for the monitoring of sodium chloride solution in the salinity relevant range of 0.4 to 0.8 M was investigated. The swelling/deswelling process induced remarkable changes in the refractive index of the coating, resulting in robust shift in the resonance wavelength of LPFG. The hydrogel-coated LPFG exhibited a sensitivity of 7 nm/M with a response time less than 1 second. There is a linear correlation between the resonance wavelength shift and the salt concentration, making quantification of measured salinity straightforward.
Solution pH is one of the most critical parameters for chemical reactions which are important for clinical, environmental or manufacturing applications. The integration of pH-responsive polyelectrolyte via layer-by-layer assembly (LbL) with long period grating (LPG) has enabled the monitoring of the pH in real time with high sensitivity at minimized volume. We show that the pH-responsive profile of the LbL/LPG platform can be tailored to specific needs depending on the deposition parameters during the LbL process. By choosing different deposition pH, weak polyelectrolytes showed either linear responsiveness or responsiveness with a reversal point at pH 4.5 over the pH range of 2-11. The most sensitive area was related to both the pKa of the chosen polyelectrolyte in the coating and the deposition pH during the LbL process. The study provides important guide to optimize and improve the sensitivity in specific pH range by selection of polyelectrolytes and/or deposition parameters. The LbL/LPG platform affords a powerful tool to study the mechanisms of the responsiveness and physiochemical properties of the polyelectrolytes.
Hospital acquired infections in indwelling device have become a life-threatening issue accompanied by the wide use of medical devices and implants. The infection process typically involves the attachment, growth and eventual assemblage of microbial cells into biofilms, with the latter exhibiting extremely higher antibiotic tolerance than planktonic bacteria. Surface constructed antimicrobial coatings offer a viable solution for bacteria responsive antibiotic strategy in medical devices such as catheter and stents. Therapeutic peptide has pioneered the field for their attractive pharmacological profile with broad antibacterial spectrum, great efficacy and long life-span. It has been a common practice to separately assess bacteria responses through commercially available activity assay kits after their exposure to antibiotic coatings, limiting the assessment of their activity in vitro with a discontinuous fashion. We developed and demonstrated an innovative all-optical lab-on-fiber optofluidic platform (LOFOP) to fill in this technical gap by allowing in situ measurement of the bacteria attachment in a continuous manner. This LOFOP allows for evaluation of drug release and resultant bacterial response by integrating glass capillary with lytic peptide-containing LbL-coated long period graing (LPG) as its core. S. aureus suspension is introduced through the assembled optofluidic platform with the capillary and the peptide-coated LPG. The efficacy of the peptide-containing coating is evaluated in situ by monitoring the attachment of bacteria and the ensuing development of biofilms using the LPG. LPG without antimicrobial coatings will be explored and compared as control.
Dielectric nanoparticle in integration with the long-period grating (LPG) is explored and its effect on the sensitivity is evaluated in the in situ monitoring of the deposition of drug delivery thin film. SiNPs were immobilized on the LPG via layer-by-layer self-assembly using poly allylamine hydrochloride (PAH). Theoretical calculation reveals that the SiNPs coating increases the evanescent field overlap in the surrounding of the LPG thus enhances its sensitivity. The increased total surface for the following thin film deposition also contributes to the enhancement of the sensitivity. Its unique capability for the in-situ monitoring of drug delivery thin film [chitosan (CHI) / Poly arylic acid (PAA) / Gentamicin sulfate (GS) /PAA]n through layer-by-layer assembly (LbL) was demonstrated with a sensitivity of 8.1 nm shift/tetralayer for LPG with 1 layer of SiNPs with 50 nm in diameter. The sensitivity enhancement of the LPG also depends heavily on the layer numbers and sizes of the SiNPs. The LPG with SiNPs of 8 layer numbers exhibits a sensitivity of only 1.2 nm shift/tetralayer. Control experiment of LPG without the SiNPs for the monitoring of [CHI/PAA/GS/PAA]n shows a sensitivity of 2.4 nm shift/tetralayer. This investigation suggests that SiNPs are effective in fine tune the optical property of the LPG. SiNPs coating thick enough can be used as an effective insulation for LPG from outer species. This investigation sets up the foundation for the development of SiNPs enabled optical fiber LPG sensor for the in-situ study of drug delivery LbL thin film.
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