Fluorescent nanodiamonds for luminescent thermometry in the biological transparency window.

Fluorescent nanodiamonds (FNDs) have attracted recent interest for biological applications owing to their biocompatibility and photostability (absence of photoblinking and bleaching). For optical thermometry, nitrogen-vacancy (NV) color centers and silicon-vacancy color centers in diamonds have demonstrated potential, where the NV has the highest sensitivity. However, NV is often excited with green light, which can cause heating and photodamage to tissues, as well as autofluorescence that decreases sensitivity. To overcome these limitations, we report temperature sensing using NV centers excited by deep red light (660 nm), plus another color center that can be excited with NIR light; the nickel (Ni) complex. The NV center measures temperature using diamond lattice expansion while the Ni complex measures temperature using phonon sideband strength.

Fluorescent nanodiamond-bacteriophage conjugates maintain host specificity.

Rapid identification of specific bacterial strains within clinical, environmental, and food samples can facilitate the prevention and treatment of disease. Fluorescent nanodiamonds (FNDs) are being developed as biomarkers in biology and medicine, due to their excellent imaging properties, ability to accept surface modifications, and lack of toxicity. Bacteriophages, the viruses of bacteria, can have exquisite specificity for certain hosts. We propose to exploit the properties of FNDs and phages to develop phages conjugated with FNDs as long-lived fluorescent diagnostic reagents. In this study, we develop a simple procedure to create such fluorescent probes by functionalizing the FNDs and phages with streptavidin and biotin, respectively. We find that the FND-phage conjugates retain the favorable characteristics of the individual components and can discern their proper host within a mixture. This technology may be further explored using different phage/bacteria systems, different FND color centers and alternate chemical labeling schemes for additional means of bacterial identification and new single-cell/virus studies.

Engineering water-tolerant core/shell upconversion nanoparticles for optical temperature sensing.

Luminescence thermometry is a promising approach using upconversion nanoparticles (UCNPs) with a nanoscale regime in biological tissues. UCNPs are superior to conventional fluorescent markers, benefiting from their autofluorescence suppression and deep imaging in tissues. However, they are still limited by poor water solubility and weak upconversion luminescence intensity, especially at a small particle size. Recently, YVO4:Er+3,Yb+3 nanoparticles have shown high efficiency upconversion (UC) luminescence in water at single-particle level and high contrast imaging in biological models. Typically, a 980-nm laser triggers the UC process in the UCNPs, which overlaps with maximum absorption of water molecules that are dominant in biological samples, resulting in biological tissues overheating and possible damaging. Interestingly, neodymium (Nd+3) possesses a large absorption cross section at the water low absorption band (808 nm), which can overcome overheating issues. In this Letter, we introduce Nd+3 as a new near-infrared absorber and UC sensitizer into YVO4:Er+3,Yb+3 nanoparticles in a core/shell structure to ensure successive energy transfer between the new UC sensitizer (Nd+3) to the upconverting activator (Er+3). Finally, we synthesized water-tolerant YVO4:Er+3,Yb+3@Nd+3 core/shell nanoparticles (average size 20 nm) with strong UC luminescence at a biocompatible excitation wavelength for optical temperature sensing where overheating in water is minimized.

In vivo diagnostics of early abiotic plant stress response via Raman spectroscopy.

Development of a phenotyping platform capable of noninvasive biochemical sensing could offer researchers, breeders, and producers a tool for precise response detection. In particular, the ability to measure plant stress in vivo responses is becoming increasingly important. In this work, a Raman spectroscopic technique is developed for high-throughput stress phenotyping of plants. We show the early (within 48 h) in vivo detection of plant stress responses. Coleus (Plectranthus scutellarioides) plants were subjected to four common abiotic stress conditions individually: high soil salinity, drought, chilling exposure, and light saturation. Plants were examined poststress induction in vivo, and changes in the concentration levels of the reactive oxygen-scavenging pigments were observed by Raman microscopic and remote spectroscopic systems. The molecular concentration changes were further validated by commonly accepted chemical extraction (destructive) methods. Raman spectroscopy also allows simultaneous interrogation of various pigments in plants. For example, we found a unique negative correlation in concentration levels of anthocyanins and carotenoids, which clearly indicates that plant stress response is fine-tuned to protect against stress-induced damages. This precision spectroscopic technique holds promise for the future development of high-throughput screening for plant phenotyping and the quantification of biologically or commercially relevant molecules, such as antioxidants and pigments.

High efficiency upconversion nanophosphors for high-contrast bioimaging.

Upconversion nanoparticles (UCNPs) are of interest because they allow suppression of tissue autofluorescence and are therefore visible deep inside biological tissue. Compared to upconversion dyes, UCNPs have a lower pump intensity threshold, better photostability, and less toxicity. Recently, YVO4: Er+3, Yb+3 nanoparticles were shown to exhibit strong up-conversion luminescence with a relatively low 10 kW cm-2 excitation intensity even in water, which makes them excellent bio-imaging candidates. Herein, we investigate their use as internal probes in insects by injecting YVO4 : Er+3, Yb+3 nanoparticles into fire ants as a biological model, and obtain 2D optical images with 980 nm illumination. High-contrast images with high signal-to-noise ratio are observed by detecting the up-conversion fluorescence as the excitation laser is scanned.