Daniela E. Achatz

Luminescent Sensing of Oxygen Using a Quenchable Probe and Upconverting Nanoparticles

Turned off by oxygen: Luminescent upconverting nanoparticles (UCNPs) of the type NaYF4:Yb,Tm are employed in an entirely new type of optical sensor for oxygen (see picture). Upon laser excitation at 980 nm, these UCNPs act as nanolamps, the blue emission of which is used to photoexcite an iridium complex dissolved in ethyl cellulose. Its green emission, in turn, is dynamically and fully reversibly quenched by molecular oxygen.

Photon upconverting nanoparticles for luminescent sensing of temperature

Photon upconverting nanoparticles convert near-infrared into visible light (anti-Stokes emission), which strongly reduces the background of autofluorescence and light scattering in biological materials. Hexagonal NaYF(4) nanocrystals doped with Yb(3+) as the sensitizer and Er(3+)/Ho(3+)/Tm(3+) as the activator display at least two emission lines that respond differently to temperature changes. The ratio of the main emission line intensities enables a self-referenced optical readout of the temperature in the physiologically relevant range from 20 to 45 °C. Upconverting nanoparticles of the type NaYF(4):Yb, Er covered by an inactive shell of NaYF(4) are bright and allow for resolving temperature differences of less than 0.5 °C in the physiological range. The optical readout of this nanoparticle-based thermometer offers many options for imaging the two-dimensional distribution of temperature.

Dual labeling of biomolecules by using click chemistry: a sequential approach.

Click by click: Dual labeling of model compounds was carried out by using copper-free and copper-mediated click chemistry in a sequential manner. This method was used to introduce two labels onto biological targets or nanoparticles, thus quickly converting them into fluorescence resonance energy transfer systems.

Luminescent chemical sensing, biosensing, and screening using upconverting nanoparticles.

Upconverting nanoparticles (UCNPs) display the unique property of converting near-infrared light (with wavelengths of typically 800-1,000 nm) into visible luminescence. Following a short introduction into the mechanisms leading to the effect, the main classes of materials used are discussed. We then review the state of the art of using UCNPs: (1) to label biomolecules such as antibodies and (synthetic) oligomers for use in affinity assay and flow assays; (2) to act as nanolamps whose emission intensity is modulated by chemical indicators, thus leading to a novel kind of chemical sensors; and (3), to act as donors in luminescence resonance energy transfer in chemical sensors and biosensors.

Surface-Modified Upconverting Microparticles and Nanoparticles for Use in Click Chemistries

A method is described for modifying the surface of upconverting microparticles (UCmuPs) and nanoparticles (UCNPs) such that they become amenable to click chemistry. Respective reagents are presented and used in both kinds of particles, either directly or in combination with tetraethoxysilane. The particles also were labeled by using the click reaction, a) with fluorophores to yield materials that have emission colors that depend on the wavelength of excitation; b) with maleinimido groups (so to obtain labels for thiols), and c) with biotin (to make them useful for affinity studies based on the biotin-streptavidin system). We believe that both the UCmuPs and UCNPs have the potential of being used in numerous areas including upconversion imaging, biolabeling, and derivatization, but also in encoding and security.

Probing the Activity of Matrix Metalloproteinase II with a Sequentially Click-Labeled Silica Nanoparticle FRET Probe

Selective double click labeling: The determination of nanomolar concentrations of matrix metalloproteinase II is made possible through the use of a nanoprobe that consists of fluorescently doped silica nanoparticles to which a FRET-based enzyme substrate has been conjugated through sequential click reactions.