Cellular analysis and detection using surface plasmon resonance imaging

Motility behavior and physiological response mechanisms of aerobic denitrifier, Enterobacter cloacae strain HNR under high salt stress: Insights from individual cells to populations

The motility behaviors at the individual-cell level and the collective physiological responsive behaviors of aerobic denitrifier, Enterobacter cloacae strain HNR under high salt stress were investigated. The results revealed that as salinity increased, electron transport activity and adenosine triphosphate content decreased from 15.75 μg O2/g/min and 593.51 mM/L to 3.27 μg O2/g/min and 5.34 mM/L, respectively, at 40 g/L, leading to a reduction in the rotation velocity and vibration amplitude of strain HNR. High salinity stress (40 g/L) down-regulated genes involved in ABC transporters (amino acids, sugars, metal ions, and inorganic ions) and activated the biofilm-related motility regulation mechanism in strain HNR, resulting in a further decrease in flagellar motility capacity and an increase in extracellular polymeric substances secretion (4.08 mg/g cell of PS and 40.03 mg/g cell of PN at 40 g/L). These responses facilitated biofilm formation and proved effective in countering elevated salt stress in strain HNR. Moreover, the genetic diversity associated with biofilm-related motility regulation in strain HNR enhanced the adaptability and stability of the strain HNR populations to salinity stress. This study enables a deeper understanding of the response mechanism of aerobic denitrifiers to high salt stress.

Polarization-Sensitive Asymmetric Scattering at the Single-Particle Scale via Surface Plasmon Resonance Microscopy

Surface plasmon resonance microscopy (SPRM), based on the scattering of single molecules at the interface, is a highly efficient analytical platform widely used in the fields of biology and chemistry. Due to the interference scattering, the imaging pattern exhibits typical parabolic tail and phase transition features, providing a quantitative means of observing the changes in the physical and chemical properties of single molecules. In this work, we reported another unique asymmetric parabolic distribution pattern resulting from polarization conversion in the experiment based on SPRM. This microscopic-level feature is derived from the switching between SPR resonant and nonresonant states. Starting from energy flux theory, we constructed an analysis model and conducted full-wave numerical simulations to verify the experimental results. Furthermore, we demonstrate that the optical rotation induced by chiral thin films can be directly measured through imaging with asymmetric features, providing valuable insights into the field of chiral materials. The quantitative interpretation of asymmetric scattering not only advances the fundamental understanding of the imaging mechanism of SPRM, but also opens up possibilities for utilizing this polarization-sensitive characteristic for single-particle detection and sensing in the future.

Modulating the plasmon-mediated silver oxidation using thiophenol molecules as monitored by in situ SERS spectroscopy

Effective charge separation is essential in plasmon-mediated photochemistry and is usually achieved by constructing plasmon-semiconductor interfaces, which is usually challenging. In this work, by monitoring the plasmon-mediated silver oxidation with in situ Raman spectroscopy, we demonstrate that the adsorbed thiophenol molecules could modulate the rate of photochemical reactions by tuning the charge separation at the plasmon-molecule interfaces. It is found that the thiophenol molecules with strong electron-withdrawing or donating functional groups could accelerate or decelerate the rate of plasmon-mediated silver oxidation, respectively. Owing to the easy tuning of the electronic structures of organic molecules via substitution, our method provides a versatile and convenient approach for the fine modulation of plasmon-mediated photochemical reactions.

Recent advances in Surface Plasmon Resonance (SPR) biosensors for food analysis: a review

Food safety is the prime area of concern that builds trust. With the prevailing advancements, it has become facile to ensure safety in almost all aspects. Technology has grown from tedious lab techniques to modern chromatographic techniques and immunoassays, progressed with more precise and rapid sensing through the advent of Biosensors. Biosensors provide an automated technology by presenting superfast, nondestructive and cost-effective detection in food analysis. SPR biosensor is an optical biosensor known for its versatility and has wider applications in food testing and analysis. It has an optical system for excitation and interrogation of surface plasmons, and a biomolecular recognition element to detect and seize the target analyte present in a sample. The optical signal detects the binding analyte, on the recognition element, which results in a change in refractive index at the surface and modifies the surface plasmons' propagation constant. SPR aids in label-free detection of various components such as adulterants, antibiotics, biomolecules, genetically modified foods, pesticides, insecticides, herbicides, microorganisms and microbial toxins in food and assures safety. The distinct advancements of SPR in food analysis have been found and discussed. The review also provides knowledge on the advantages and the key challenges encountered by SPR.

Adaptation mechanism of aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle stresses

The adaptation mechanism of a wild type (WT) and resistant type (Re) strain of the aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle (NP) stresses was investigated. The results showed that Re maintained higher nitrite reductase (NIR) and nitrate reductase (NR) activities and showed lower increment of reactive oxygen species (ROS) than WT, under ZnO NP stresses. The affinity constant (K_A) of WT to Zn²⁺ was 5.06 times that of Re, indicating that Re was more repulsive to Zn²⁺ released by ZnO NPs. Transcriptomic analysis revealed that the up-regulation of the nitrogen metabolism of Re helped maintain NIR and NR activities, that the enhancement of purine metabolism lowered the intracellular ROS increment, and that the up-regulation of cationic antimicrobial peptide resistance contributed to the lower K_A of Re to Zn²⁺. These findings provided new insights into the adaptation mechanism of aerobic denitrifying bacteria to ZnO NPs.

Layer analysis of axial spatial distribution of surface plasmon resonance sensing

The spatial distribution detection and characterization of multi-adsorption layers, biomembranes, and cells are important techniques to study biomolecular properties and mechanisms. Using the surface plasmon resonance (SPR) technology, we investigated the spatial characteristics, penetration mechanism, and detection depth of the interaction between evanescent waves and a complex medium. In addition, parameters correlated with the axial spatial distribution were analyzed. We found that the spatial refractive-index distribution of an axial layered model has a unique correlation with the following three characteristic parameters: resonance angle at different wavelengths, first-derivative extreme-point of the angular spectrum, and effective refractive index. A new layer-analysis, based on wavelength-scanning angle interrogation (WSAI), was introduced to enable refractive-index measurements in an axial spatial medium. This new method extends the detection capabilities of SPR sensors and provides a more accurate analysis method for interaction events within an evanescent field.

Imaging the Microprocesses in Biofilm Matrices

Biofilms, which are aggregates of microorganisms and extracellular matrices, widely colonize natural water bodies, wastewater treatment systems, and body tissues, and have vital roles in water purification, biofouling, and infectious diseases. Recently, multiple imaging modalities have been developed to visualize the morphological structure and material distribution within biofilms and to probe the microprocesses in biofilm matrices, including biofilm formation, transfer and metabolism of substrates, and cell-cell communication. These technologies have improved our understanding of biofilm control and the fates of substrates in biofilms. In this review, we describe the principles of various imaging techniques and discuss the advantages and limitations of each approach to characterizing microprocesses in biofilm matrices.