A new approach is presented for analysis of microplastics in environmental samples, based on selective fluorescent staining using Nile Red (NR), followed by density-based extraction and filtration. The dye adsorbs onto plastic surfaces and renders them fluorescent when irradiated with blue light. Fluorescence emission is detected using simple photography through an orange filter. Image-analysis allows fluorescent particles to be identified and counted. Magnified images can be recorded and tiled to cover the whole filter area, allowing particles down to a few micrometres to be detected. The solvatochromic nature of Nile Red also offers the possibility of plastic categorisation based on surface polarity characteristics of identified particles. This article details the development of this staining method and its initial cross-validation by comparison with infrared (IR) microscopy. Microplastics of different sizes could be detected and counted in marine sediment samples. The fluorescence staining identified the same particles as those found by scanning a filter area with IR-microscopy.
We demonstrate, on the example of trypsin, the use of water-soluble molecularly imprinted polymer microgels as specific enzyme inhibitors. Using a strong anchoring monomer, methacryloylaminobenzamidine, the growing polymer chains are confined to close proximity of the substrate recognition site of our model enzyme. The microgels bind selectively trypsin over other proteins of similar size and molecular weight, and show competitive inhibition of trypsin with an inhibition constant K(i) of 79 nM, making them more potent inhibitors than the low molecular-weight competitive inhibitor benzamidine by almost 3 orders of magnitude. We believe that these tailor-made materials with biological activity have potential for future drug development that extends beyond enzyme inhibition.
Molecularly imprinted
polymers (MIPs) are tailor-made chemical
receptors that recognize and
bind target molecules with a high affinity and selectivity. MIPs came
into the spotlight in 1993 when they were dubbed “antibody
mimics,” and ever since, they have been widely studied for
the extraction or trapping of chemical pollutants, in immunoassays,
and for the design of sensors. Owing to novel synthesis strategies
resulting in more biocompatible MIPs in the form of soluble nanogels,
these synthetic antibodies have found favor in the biomedical domain
since 2010, when for the first time, they were shown to capture and
eliminate a toxin in live mice. This review, covering the years 2015–2020,
will first describe the rationale behind these antibody mimics, and
the different synthesis methods that have been employed for the preparation
of MIPs destined for in vitro and in vivo targeting and bioimaging
of cancer biomarkers, an emerging and fast-growing area of MIP applications.
MIPs have been synthesized for targeting and visualizing glycans and
protein-based cell receptors overexpressed in certain diseases, which
are well-known biomarkers for example for tumors. When loaded with
drugs, the MIPs could locally kill the tumor cells, making them efficient
therapeutic agents. We will end the review by reporting how MIPs themselves
can act as therapeutics by inhibiting cancer growth. These works mark
a new opening in the use of MIPs for antibody therapy and even immunotherapy,
as materials of the future in nanomedicine.
By using porous silica gel as a solid support, template molecules can be immobilized to give a novel approach to molecular imprinting in polymers. Polymerizable, functional monomers assemble around a template (such as theophylline, see picture). Following polymerization, this support is sacrificed by dissolving in HF. The remaining polymer shows a specific binding capacity for theophylline, but not for related compounds, such as theobromine and caffeine. All binding sites are uniformly oriented and located at the surface of the polymer.
Noncovalent molecular imprinting of a synthetic polymer with the herbicide 2,4-dichlorophenoxyacetic acid has been achieved in the presence of the polar solvents methanol and water. Formation of the prearranged complex relied on hydrophobic and ionic interactions between the template and the functional monomer 4-vinylpyridine. The polymer obtained binds the original template with an appreciable selectivity over structurally related compounds. The potential use of micrometer-sized imprinted polymer particles as the recognition element in a radioligand binding assay for 2,4-dichlorophenoxyacetic acid is demonstrated.
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