title: Proteolytic assays on quantum-dot-modified paper substrates using simple optical readout platforms.
abstract: Paper-based assays are a promising diagnostic format for point-of-care applications, field deployment, and other low-resource settings. To date, the majority of efforts to integrate nanomaterials with paper-based assays have utilized gold nanoparticles. Here, we show that semiconductor quantum dots (QDs), in combination with Förster resonance energy transfer (FRET), are also suitable nanomaterials for developing paper-based assays. Paper fibers were chemically modified with thiol ligands to immobilize CdSeS/ZnS QDs, the QDs were self-assembled with dye-labeled peptides to generate efficient FRET, and steady-state and fluorescence lifetime imaging microscopy (FLIM) were used for characterization. Peptides were selected as substrates for three different proteases and a series of kinetic assays for proteolytic activity was carried out, including multiplexed assays and pro-enzyme activation assays. Quantitative results were obtained within 5-60 min at levels as low as 1-2 nM of protease. These assays were possible using simple optical readout platforms that did not negate the low cost, ease of use, and overall accessibility advantages of paper-based assays. A violet light-emitting diode (LED) excitation source and color imaging with either a digital camera, consumer webcam, or smartphone camera were sufficient for analysis on the basis of a red/green color intensity ratio. At most, a universal serial bus (USB) connection to a computer was required and the instrumentation cost orders of magnitude less than that typically utilized for in vitro bioanalyses with QDs. This work demonstrates that QDs are valuable probes for developing a new generation of paper-based diagnostics.
authors: Department of Chemistry, University of British Columbia , 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.
authors: Eleonora
authors: E
authors: Petryayeva
authors: W Russ
authors: WR
authors: Algar
mesh_terms: D000595:Amino Acid Sequence; D002918:Chymotrypsin / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods*; D008969:Molecular Sequence Data; D010209:Paper; D017433:Protein Structure, Secondary; D059748:Proteolysis; D045663:Quantum Dots / Q000737:chemistry*; D014357:Trypsin / Q000032:analysis* / Q000737:chemistry / Q000235:genetics
chemical_list: D002918:Chymotrypsin; D014357:Trypsin