Biomedical Engineering Reference
In-Depth Information
lysozyme sensor using protein-imprinted MIP NPs [ 94 ]. MIP NPs of 50 nm in
diameter were synthesized by mini-emulsion polymerization and physically depos-
ited on a QCM crystal by solvent evaporation. The imprinted sensor exhibited a
detection limit of 1.2 ng mL 1 for lysozyme in the analysis of chicken egg-white
samples. The system could be used in up to four consecutive measurements. The
same lysozyme-imprinted MIP NPs were also used in a surface plasmon resonance
(SPR) sensor [ 95 ]. The SPR sensor exhibited fast response times with a 1000-fold
lower detection limit than the QCM sensor.
One of the first MIP NPs-based assays reported in the literature was described by
Haupt and coauthors [ 96 ]. The MIP NPs were imprinted with 2,4-dichloro-
phenoxyacetic acid (2,4-D), and used with structurally related fluorescent, chemi-
luminescent or electrochemical probes to quantify the amount of bound analyte
[ 97 ]. The detection limit achieved was 100 nM. However the assay showed
significant cross-reactivity with 2,4-D structural analogues. Nevertheless, these
first results paved the way for the use of MIP nanoparticles in pseudo-
immunoassays. Ye and coauthors synthesized 200-300 nm MIP nanoparticles
imprinted with THO and 17
-estradiol (E2) by precipitation polymerization and
used them in a first MIP NPs-based radioimmunoassay [ 65 , 98 ]. The authors were
able to quantify templates down to concentrations of 0.1 and 0.01
b
gmL 1 for THO
and E2, respectively, even in the presence of competing structural analogues. The
authors later improved this assay system by adding a “scintillation monomer”
hydroxymethyl-2,5-diphenyloxazole acrylate and divinylbenzene into the prepara-
tion [ 99 , 100 ]. The binding signal was generated by proximity energy transfer,
which arose from the specific binding of a tritium-labeled template ( S -propranol).
In this approach there was no need to remove the unbound labeled ligand, because
the latter was in solution and therefore too distant from the scintillation monomer to
generate a signal. MIP nanoparticles exhibited discrete enantioselectivity. How-
ever, the MIP NPs did not perform well in aqueous environment and relied on
“unpopular” radioactive isotopes. Surugiu and coauthors developed an ELISA-like
assay based on MIP NPs imprinted with 2,4-D. The target analyte was labeled with
tobacco peroxidase as an enzymatic probe and used to detect the template either
colorimetrically or by chemiluminescence [ 101 ]. In both cases the competition
between free template and analogue was monitored in solution, allowing quantifi-
cation of 2,4-D to 1
m
gmL 1 . Unfortunately the cross-reactivity of the assay to
structural analogues was quite high. Later the same MIP NPs were immobilized on
microtiter plate wells using polyvinyl alcohol (PVA) as glue. Detection of chemi-
luminescence from the competition reaction was performed using a CCD camera
[ 102 ]. The detection limit of the assay was decreased to 34 nM. As in the previous
cases, some cross-reactivity was exhibited, especially when compared to the same
assay performed using antibodies. P´rez and coauthors designed an immunoprecip-
itation like assay for cholesterol using surface-imprinted MIP nanoparticles
prepared by core-shell emulsion polymerization [ 103 ]. MIP nanoparticles exhibited
uniform morphology and small diameters (60 nm). The addition of a multi-ligand
template, polyethylene glycol (PEG)-bis-cholesterol, was able to flocculate the MIP
particles, while mono-ligand template did not give rise to these effects (Fig. 7 ).
m
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