Seite - 18 - in Cancer Nanotheranostics - What Have We Learnd So Far?

Condeetal. Biofunctionalizationandsurfacechemistryof inorganicnanoparticles FIGURE6 |Quantumdotproteinbiosensors. (A)Schematic showing the commondesign, chemical andsensingelements, includingFRET-based biosensors: (1)peptidemodularity, (2)peptide labeling, (3)attachment toQDs, and (4)FRET-basedsensingforboththecaspase3proteolyticsensor (left)and Ca2+ sensor (right). The4-pendant carboxyl groups that interactwithCa2+ ionsareshown in redon theCaRbCl structure.Within theCa2+ sensor peptidesequence,Aib is thesynthetic aminoacidα-aminoisobutyric acid. Reactivedyestructuresareshownwhereappropriatealongwith thechemical linkagesattaching themto thepeptides. (B)Representative, superimposed spectracollectedfrom550nmemittingQDdonorssurfacefunctionalizedwith 85:15DHLAPEG600-COOH/DHLA-PEG750-OMe ligandsandcovalently conjugated to increasingmolar ratiosofTexasRed-labeledsubstratepeptide. Samplesexcitedat350nm. (C)Proteolytic assaydata fromexposinga constant concentrationof550nmemittingQDsconjugated to4TexasRed substratepeptides toaconstantconcentrationofcaspase3enzyme.Derived KmandVmaxvaluesaregiven.AnR2=0.98wasobtained for thefittingof thecurve. (D)Representative, superimposed, anddeconvolutedspectra collected from580nmemittingQDdonorsself-assembledwith increasing CaRbCl-acceptor labeledpeptides.Sampleswereexcitedat350nm. (E)Normalizedacceptor/donorPLarea ratios for580nmQDsself-assembled with∼2CaRbCl-acceptor labeledpeptidesexposed toselected ionic materials. The ratio fromthenativeunexposedsensorwasset toan initial valueof1 for comparisonpurposes (Prasuhnet al., 2010).Reproducedwith permission fromPrasuhnet al. (2010),Copyright2013. When using enzyme-based biosensors the main concern is reusability of the enzyme. Khoshnevisan et al. reported the use ofMNPs to circumvent this dilemmawhenusing cellulase. The enzymewas incubatedwith theMNPsandbindingconfirmedby FT-IR.The authors show that immobilization grants higher sta- bility totheenzyme, thusconfirmingthat theuseofMNPsinthis type of biosensors can be of great benefit (Khoshnevisan et al., 2011). www.frontiersin.org July2014 |Volume2 |Article48 | 18