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Ultrasensitive tantalum oxide nano-coated long-period gratings for detection of various biological targets
摘要： In this work we discussed a label-free biosensing application of long-period gratings (LPGs) optimized in refractive index (RI) sensitivity by deposition of thin tantalum oxide (TaOx) overlays. Comparing to other thin film and materials already applied for maximizing the RI sensitivity, TaOx offers good chemical and mechanical stability during its surface functionalization and other biosensing experiments. It was shown theoretically and experimentally that when RI of the overlay is as high as 2 in IR spectral range, for obtaining LPGs ultrasensitive to RI, the overlay’s thickness must be determined with subnanometer precision. In this experiment the TaOx overlays were deposited using Atomic Layer Deposition method that allowed for achieving overlays with exceptionally well-defined thickness and optical properties. The TaOx nano-coated LPGs show RI sensitivity determined for a single resonance exceeding 11,500 nm/RIU in RI range nD=1.335-1.345 RIU, as expected for label-free biosensing applications. Capability for detection of various in size biological targets, i.e., proteins (avidin) and bacteria (Escherichia coli), with TaOx-coated LPGs was verified using biotin and bacteriophage adhesin as recognition elements, respectively. It has been shown that functionalization process, as well as type of recognition elements and target analyte must be taken into consideration when the LPG sensitivity is optimized. In this work optimized approach made possible detection of small in size biological targets such as proteins with sensitivity reaching 10.21 nm/log(ng/ml).
关键词： protein detection,label-free biosensing,optical fiber sensor,tantalum oxide,bacteria detection,long-period grating,atomic layer deposition
更新于2025-11-28 14:23:57
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A Nanostructured Gold/Graphene Microfluidic Device for Direct and Plasmonic-Assisted Impedimetric Detection of Bacteria
摘要： Hierarchical 3D gold nano-micro islands (NMIs) are favourably structured for direct and probe-free capture of bacteria in optical and electrochemical sensors. Moreover, their unique plasmonic properties make them a suitable candidate for plasmonic-assisted electrochemical sensors, yet the charge transfer needs to be improved. In the present study, we propose a novel plasmonic-assisted electrochemical impedimetric detection platform based on hybrid structures of 3D gold NMIs and graphene (Gr) nanosheets for probe-free capture and label-free detection of bacteria. The inclusion of Gr nanosheets significantly improves the charge transfer, addressing the central issue of using 3D gold NMIs. Notably, the 3D gold NMIs/Gr detection platform successfully distinguishes between various types of bacteria including Escherichia coli (E. coli) K12, Pseudomonas putida (P. putida) and Staphylococcus epidermidis (S. epidermidis) when electrochemical impedance spectroscopy is applied under visible light. We show that distinguishable and label-free impedimetric detection is due to dissimilar electron charge transfer caused by various sizes, morphologies, and compositions of the cells. In addition, the finite-difference time-domain (FDTD) simulation of the electric field indicates the intensity of charge distribution at the edge of the NMI structures. Furthermore, the wettability studies demonstrated that contact angle is a characteristic feature of each type of captured bacteria on the 3D gold NMIs, which strongly depends on the shape, morphology, and size of the cells. Ultimately, exposing the platform to various dilutions of the three bacteria strains, revealed the ability to detect dilutions as low as ~20 CFU/mL in a wide linear range of detection of 2(cid:3)101-105, 2(cid:3)101-104 and 1(cid:3)102-1(cid:3)105 CFU/mL for E. coli, P. putida, and S. epidermidis, respectively. The proposed hybrid structure of 3D gold NMIs and Gr combined by novel plasmonic and conventional impedance spectroscopy techniques open interesting avenues in ultrasensitive label-free detection of bacteria with low cost and high stability.
关键词： Label-free bacteria detection,Hierarchical gold nano-micro islands,Surface properties,Impedance spectroscopy,plasmonic-assisted electrochemical detection platform
更新于2025-09-23 15:19:57
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Rapid label-free detection of intact pathogenic bacteria <i>in situ via</i> surface plasmon resonance imaging enabled by crossed surface relief gratings
摘要： The unique plasmonic energy exchange occurring within metallic crossed surface relief gratings (CSRGs) has recently motivated their use as biosensors. However, CSRG-based biosensing has been limited to spectroscopic techniques, failing to harness their potential for integration with ubiquitous portable electronics. Here, we introduce biosensing via surface plasmon resonance imaging (SPRi) enabled by CSRGs. The SPRi platform is fully integrated including optics and electronics, has bulk sensitivity of 613 Pixel Intensity Unit (PIU)/Refractive Index Unit (RIU), a resolution of 10?6 RIU and a signal-to-noise ratio of ～33 dB. Finite-Difference Time-Domain (FDTD) simulations confirm that CSRG-enabled SPRi is supported by an electric field intensity enhancement of ～30 times, due to plasmon resonance at the metal-dielectric interface. In the context of real-world biosensing applications, we demonstrate the rapid (<35 min) and label-free detection of uropathogenic E. coli (UPEC) in PBS and human urine samples for concentrations ranging from 103 to 109 CFU mL?1. The detection limit of the platform is ～100 CFU mL?1, three orders of magnitude lower than the clinical detection limit for diagnosis of urinary tract infection. This work presents a new avenue for CSRGs as SPRi-based biosensing platforms and their great potential for integration with portable electronics for applications requiring in situ detection.
关键词： crossed surface relief gratings,portable electronics,biosensing,pathogenic bacteria detection,surface plasmon resonance imaging
更新于2025-09-23 15:19:57
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Mobile Based in Situ Detection of Live/Dead and Antibiotic Resistant Bacteria by Silver Nanorods Array Sensor Fabricated by Glancing Angle Deposition
摘要： The rapid in-situ detection of viability of bacteria is essential for human health and environmental care. It has become one of the biggest needs in biological and medical sciences to prevent infections and diseases, which usually occur in hospitals and field clinics. Nowadays, antibiotic resistance (ABR) has been grown as one of the world’s acutest public health problems, which requires a quick and efficient solution. Here, we demonstrate an easy, sensitive, user-friendly, portable, cost effective and time saving approach for detection of live, dead and drug resistant bacteria. Most of the organisms are found to produce H2S gas by their metabolism system. The endogenous H2S evolution was targeted to differentiate between live and dead as well as ABR bacteria. The silver nanorods (AgNRs) arrays sensors were fabricated by glancing angle deposition technique. The colorimetric and water wettability (contact angle) features of as-synthesized AgNRs were found to be highly sensitive and selective for hydrogen sulfide (H2S) gas. E.coli, P. aeruginosa, B. subtilis and S. aureus were used as the model organisms for this study. A drastic visible change in color as well as wetting properties of AgNRs array was observed. To make it easy, a user friendly and field deployable android based mobile app ‘Colorimetric Detector’ was developed. This dual mode detection is facile, inexpensive and can be easily scaled-up in the field of disease diagnosis.
关键词： mobile app,colorimetric detection,silver nanorods,antibiotic resistance,bacteria detection,H2S gas
更新于2025-09-11 14:15:04
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Direct Detection of Bacteria Using Positively-charged Ag/Au Bimetallic Nanoparticles: A Label-Free SERS Study Coupled with Multivariate Analysis
摘要： Rapid detection and discrimination of pathogenic bacteria for food safety, environmental pollution, medical diagnoses, and chemical and biological threats remains a considerable challenge. In the present work, we demonstrate positively charged Ag/Au bimetallic nanoparticles (Ag/Au bmNPs) as a potential surface-enhanced Raman scattering (SERS) substrate for label-free detection and discrimination of three bacteria, viz., Escherichia coli, Salmonella typhimurium and Bacillus subtilis with excellent reproducibility. The approach relies on a priori synthesis of Ag/Au bmNPs and subsequent SERS studies on bacteria. The positive surface charge on Ag/Au bmNPs offers significant advantages of short acquisition time at very low power, high sensitivity, and simple operating procedure without the need of very specific procedures/protocols used to capture the bacteria. The reproducible and specific intrinsic fingerprint of the cell wall and intracellular components of three bacteria obtained by label-free SERS enables precise discrimination and classification of three bacteria using multivariate analysis such as principal component analysis and canonical discriminant analysis.
关键词： SERS,multivariate analysis,Optical,Magnetic,label-free study,and Hybrid Materials,bacteria detection,Ag/Au bimetallic nanoparticles,Plasmonics
更新于2025-09-11 14:15:04
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Magneto-fluorescent microbeads for bacteria detection constructed from superparamagnetic Fe <sub/>3</sub> O <sub/>4</sub> nanoparticles and AIS/ZnS quantum dots
摘要： The efficient and sensitive detection of pathogenic microorganisms in aqueous environments such as water used in medical applications, drinking water, and cooling water of industrial plants requires simple and fast methods suitable for multiplexed detection such as flow cytometry (FCM) with optically encoded carrier beads. For this purpose, we combine fluorescent Cd-free Ag-In-S ternary quantum dots (t-QDs) with fluorescence lifetimes (LTs) of several hundred nanoseconds and superparamagnetic Fe3O4 nanoparticles (SPIONs) with mesoporous CaCO3 microbeads to a magneto-fluorescent bead platform that can be surface-functionalized with bioligands such as antibodies. This inorganic bead platform enables immuno-magnetic separation, target enrichment, and target quantification with optical readout. The beads can be detected with steady-state and time-resolved fluorescence microscopy and flow cytometry (FCM). Moreover, they are suited for readout by time gated emission. In the following, the preparation of these magneto-fluorescent CaCO3 beads, their spectroscopic and analytic characterization, and their conjugation with bacteria-specific antibodies are presented as well as proof-of-concept measurements with Legionella pneumophila including cell cultivation and plating experiments for bacteria quantification. Additionally, the possibility to discriminate between the long-lived emission of the LT-encoded capture and carrier CaCO3 beads and the short-lived emission of the dye-stained bacteria with time-resolved fluorescence techniques and single wavelength excitation is demonstrated.
关键词： AIS/ZnS quantum dots,flow cytometry,magneto-fluorescent microbeads,time-resolved fluorescence,superparamagnetic Fe3O4 nanoparticles,bacteria detection
更新于2025-09-11 14:15:04