Enzyme-linked immunoassay (ELISA) is highly specific and selective towards target molecules and is convenient for on-site detection. However, in many cases, lack of high sensitivity makes it hard to reveal a significant colorimetric signal for detecting a trace amount of target molecules. Thus, analytical instruments are required for detection, which limits the application of ELISA for on-site detection. In the present study, a highly sensitive and naked-eyed detectable colorimetric biosensor for chloramphenicol (CAP) was prepared by incorporating ELISA onto surfaces of microporous and nanofibrous membranes. The high specific surface areas of the nanofibers significantly increased the number of antibodies covalently linked onto the fiber surfaces and binding capacity of the sensor with antigens present in a sample. With such an integration, the sensitivity of the ELISA sensor was dramatically increased, and a trace number of targets could reveal a naked-eye detectable color. The immunoassay sensor exhibited a significant naked-eye distinguishable color to chloramphenicol (CAP) at 0.3 ng/ mL. The successful design and fabrication of the nanofibrous membrane immunoassay sensor provide new paths towards the development of on-site inspection sensors without the assistance from any instrument.
An intrinsically hydrophilic nanofibrous
membrane with chlorine
rechargeable biocidal and antifouling functions was prepared by using
a combination of chemically bonded N-halamine moieties
and zwitterionic polymers (PEI-S). The designed nanofibrous membrane,
named as PEI-S@BNF-2 h, can exhibit integrated features of reduced
bacterial adhesion, rechargeable biocidal activity, and easy release
of killed bacteria by using mild hydrodynamic forces. The representative
functional performances of the PEI-S@BNF-2 h membrane include high
active chlorine capacity (>4000 ppm), large specific surface area,
ease of chlorine rechargeability, long-term stability, and exceptional
biocidal activity (99.9999% via contact killing). More importantly,
the zwitterionic polymer moieties (PEI-S) brought robust antifouling
properties to this biocidal membrane, therefore reducing the biofouling-biofilm
effect and prolonging the lifetime of the filtration membrane. These
attributes enable the PEI-S@BNF-2 h nanofibrous membrane to effectively
disinfect the microbe-contaminated water with high fluxes (10,000
L m–2 h–1) and maintain itself
clean for a long-term application.
An ultrasensitive and portable colorimetric enzyme-linked immunosorbent assay (ELISA) sensor for antibiotics was fabricated by immobilizing antibodies inside the largely porous and highly hydrophilic nanofibrous membranes. Different from regular electrospun nanofibrous membranes where antibodies may frequently be blocked by the heterogeneous porous structure and sterically crowded loaded on the surface, the controlled microporous structure and increased hydrophilicity of nanofibrous membranes could improve the diffusion properties of antibodies, reduce the sterically crowding effect, and dramatically improve the sensitivity of the membrane-based ELISA. The limitation of detection (LOD) for chloramphenicol (CAP) reached 0.005 ng/mL, around 200 times lower than the conventional paper-based ELISA, making quantitative analysis and portable on-site detection achievable via the use of smartphones. The successful design and fabrication of the nanofibrous membrane-based ELISA with novel features overcome the structural drawbacks of regular electrospun nanofibrous membranes and provide new paths to develop highly sensitive on-site detection of hazardous chemical agents.
Photoactivities and photoinduced
antibacterial functions of two
vitamin B2 (VB2) derivatives, riboflavin (RF)
and flavin mononucleotide (FMN), were investigated by computational
modeling and various experimental evaluations. Under photoirradiation,
the ground state of both VB2 derivatives could be excited
to generate different reactive oxygen species (ROS) by undergoing
different reaction paths. The formed ROS could nonselectively inactivate
microorganisms. However, both RF and FMN exhibited negligible photoinduced
antimicrobial activity in phosphate-buffered saline (PBS) solutions
even at high concentrations. The study revealed that the affinity
of both RF and FMN to microorganisms in different application media
plays a key role due to the very short lifetime of the generated ROS.
The speculation was proven by the preparation of a poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibrous membrane
blended with RF or FMN, which could enhance the contact of the agents
with microorganisms. The fabricated nanofibrous membranes containing
both VB2 derivatives (VBNFMs) showed great photoinduced
antibacterial activity against Gram-negative Escherichia
coli (E. coli) (99.999%
bacterial reduction) and Gram-positive Listeria innocua (L. innocua) (99% bacterial reduction)
under 20 min of ultra-violet A irradiation. The photoinduced antimicrobial
performances of RF/PVA-co-PE and FMN/PVA-co-PE nanofibrous membranes were comparable. Interestingly,
the durability of the photoinduced antibacterial functions of the
prepared VBNFMs was questionable, due to the photodegradation of VB2 in nanomaterials.
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