Selective, reversible, reagentless maltose biosensing with core–shell semiconducting nanoparticles

Abstract

Reagentless and reversible maltose biosensors are demonstrated using ZnS coated CdSe (CdSe@ZnS) nanoparticle emission intensities. This method is based on electron transfer quenching of unimolecular protein-CdSe@ZnS nanoparticle assemblies, which is provided by a protein-attached Ru(II) complex. This Ru(II) complex is presumed to reduce a valence band hole of the CdSe@ZnS excited state by tunneling through the ZnS overcoating. The Ru(II) complex mediated quenching of CdSe@ZnS nanoparticle emission was only decreased 1.2-fold relative to the CdSe nanoparticle systems. While four different Ru(II) complex attachment sites provided different amounts of nanoparticle emission quenching (1.20 to 1.75-fold decrease), all of these attachment sites yielded maltose-dependent intensity changes (1.1 to 1.4-fold increase upon maltose addition). Maltose dissociation constants for these four biosensing systems range from 250 nM to 1.0 microM, which are similar to the maltose-maltose binding protein dissociation constant that these sensors are based on. The increased fluorescence intensity was found to only occur in the presence of maltose. Furthermore, the ability of these reagentless protein-nanoparticle assemblies to perform maltose biosensing reversibly is demonstrated with the addition of alpha-glucosidase. Three 50 microM maltose additions after alpha-glucosidase addition showed increases of 2.2 microM, 600 nM, and 150 nM maltose. This result demonstrates a fluorometric method for examining alpha-glucosidase activity. Using maltose binding protein to control Ru(II) complex interactions with CdSe@ZnS nanoparticle surfaces provide a novel class of highly fluorescent, photostable biosensors that are selective for maltose.

Quantum Dots in Bioanalysis: A Review of Applications across Various Platforms for Fluorescence Spectroscopy and Imaging

“…Another expected advantage of charge transfer is an exponential dependence of the quenching efficiency on the distance between the QD and redox-active moiety. 175 This sensitivity has been borne out in several unimolecular sensing constructs developed by Benson's group for the detection of maltose, 195,196 palmitate, 197 lead, 198 and thrombin. 175 These constructs have been reviewed elsewhere 16 and were based on conformational changes associated with receptor proteins or oligonucleotides/ aptamers upon binding with their cognate target.…”

Fluorescence Quenching of Quantum Dots by DNA Nucleotides and Amino Acids

“…[11][12][13] Influence of various compounds on the fluorescence emission properties of QD raised a strong interest in their use as fluorescent sensors, like the quenching by metal ions, [12,14,15] gold nanoparticles, [16,17] and various other compounds. [18][19][20][21][22][23] Further studies focussed on the oxidation of QD, [24] or photo-induced charge transfer, [11] and also on the influence of experimental conditions, such as temperature or pH. [7,25,26] Herein we present a systematic study on the interaction of nucleotides and amino acids with QD, which occasionally leads to a significant quenching of fluorescence intensity.…”

Engineered Derivatives of Maltose-Binding Protein

“…A change in redox potential dependent on maltose could be measured by monitoring current as a function of voltage. This general idea was extended to MBP-Ru(II) tethered to ZnS coated CdSe nanoparticles, where the photoluminescense of the nanoparticles responds to the MBP conformational shift (Sandros et al, 2005, Sandros et al, 2006. Park et al took a different approach, fabricating an ion sensitive field effect transistor by coating a standard CMOS transistor with nickel and assembling MBP-His on the surface (Park, H. J. et al, 2009a).…”