Masfer H. Alkahtani

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.

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

Significance Feeding a population of 9 billion in 2050 coupled with the changing climate and environmental stresses motivate us to develop advances in plant science and technology. We present a high-throughput plant phenotyping platform for detection of abiotic stress. The proposed Raman spectroscopic technique for high-throughput stress phenotyping and early stress detection in vivo improves sensitivity with the ability to interrogate individual molecules simultaneously in plants. This technology holds promise for mobile automated systems and precision agriculture. 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.

Fluorescent nanodiamonds and their use in biomedical research

Nanodiamonds containing color-centers produce non-quenching fluorescence that is easily detected. This makes them useful for cellular, proteomic and genomic applications. However, fluorescent nanodiamonds have yet to become popular in the biomedical research community as labeling reagents. We discuss production of nanodiamonds with distinct color-centers and assess their biocompatibility and techniques for bioconjugation. Fluorescent diamonds were fabricated by electron irradiation of high-pressure, high-temperature micron-sized diamonds which generated diamonds with vacancy-related defects (V). These diamonds were annealed to create nitrogen vacancy (NV)-centers then following a milling step were fractionated into nanoparticle sizes of 30, 60, and 95 nm. Optical characterization of Vand NV-center diamonds demonstrated fluorescence in two distinct green and red channels, respectively. In vitro studies demonstrated that these nanodiamonds are biocompatible and readily taken up by murine macrophage cells. Quantification of NV-center nanodiamond uptake by flow cytometry, showed that uptake was independent of nanodiamond size. Confocal microscopy demonstrated that NV-center nanodiamonds accumulate within the cytoplasm of these cells. NV-center nanodiamonds were then conjugated with streptavidin using a short polyethylene chain as linker. Conjugation was confirmed via a catalytic assay employing biotinylated-horseradish peroxidase. We present a technique for large-scale production of biocompatible conjugated V- or NV-center nanodiamonds. Functional testing is essential for standardization of fluorescent nanodiamond bioconjugates and quality control. Large-scale production of bioconjugated fluorescent nanodiamonds is crucial to their development as novel tools for biological and medical applications.

Germanium-Vacancy Color Center in Diamond as a Temperature Sensor

We present high-resolution, all-optical thermometry based on ensembles of germanium-vacancy (GeV) color center in diamond and implement this method of thermometry in the fiber-optic format. Due to the unique properties of diamond, an all-optical approach using this method opens a way to produce back-action-free temperature measurements with resolution below 0.1 K in a wide range of temperatures.

Nanometer-scale luminescent thermometry in bovine embryos

Luminescent nanothermometry is a powerful tool that can precisely monitor temperature changes in animal embryos. Among the most sensitive nanoluminescent temperature sensors are fluorescent nanodiamonds (FNDs), having nitrogen-vacancy color centers, and lanthanide-ion-doped upconversion nanoparticles (UCNPs). Here, we investigate their use as nanothermometers inside bovine embryos. The motivation for using both FNDs and UCNPs to measure temperature is to avoid the question of sensor confusion by the local cellular environment. Specifically, by simultaneously measuring temperature using two different modalities having different physics, it is possible to greatly improve the measurement confidence, thereby directly addressing the recent controversy surrounding temperature measurements in living organisms.

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.

In situ Investigation of the Growth of a Tribofilm Consisting of NaYF4 Fluorescent Nanoparticles

ABSTRACT Tribofilms play a vital role in protecting lubricated surfaces in mechanical systems in motion. To date, understanding tribofilms has been mostly based on ex situ analysis. This research investigates the kinetics of a tribofilm formed on a pair of bearing steels (E52100). Strategically selected illuminative nanoparticles of NaYF4 were added to a base oil in order to enable their tracking. Electrical conductivity was monitored during sliding that was found to be linked to the state of the interface and the tribofilm. Further characterization identified tribochemical reaction products of Y2O3 that exhibited superior tribological performance. In comparison with mineral oil as the base lubricant, the addition of NaYF4 resulted in a reduction in wear of 82%. This work discovered three stages in tribofilm formation: running in, reactive, and growth. Interestingly, the formation of a tribofilm was dominated more by frictional force than applied load. This is significant because we can now use alternative strategies to generate quality tribofilms.

Developing upconversion nanoparticle-based smart substrates for remote temperature sensing

Recent developments in understanding of nanomaterial behaviors and synthesis have led to their application across a wide range of commercial and scientific applications. Recent investigations span from applications in nanomedicine and the development of novel drug delivery systems to nanoelectronics and biosensors. In this study, we propose the application of a newly engineered temperature sensitive water-based bio-compatible core/shell up-conversion nanoparticle (UCNP) in the development of a smart substrate for remote temperature sensing. We developed this smart substrate by dispersing functionalized nanoparticles into a polymer solution and then spin-coating the solution onto one side of a microscope slide to form a thin film substrate layer of evenly dispersed nanoparticles. By using spin-coating to deposit the particle solution we both create a uniform surface for the substrate while simultaneously avoid undesired particle agglomeration. Through this investigation, we have determined the sensitivity and capabilities of this smart substrate and conclude that further development can lead to a greater range of applications for this type smart substrate and use in remote temperature sensing in conjunction with other microscopy and spectroscopy investigations.

Fluorescent nanodiamonds: past, present, and future

Abstract Multi-color fluorescent nanodiamonds (FNDs) containing a variety of color centers are promising fluorescent markers for biomedical applications. Compared to colloidal quantum dots and organic dyes, FNDs have the advantage of lower toxicity, exceptional chemical stability, and better photostability. They can be surface functionalized by techniques similar to those used for other nanoparticles. They exhibit a variety of emission wavelengths from visible to near infrared, with narrow or broad bandwidths depending on their color centers. In addition, some color centers can detect changes in magnetic fields, electric fields, and temperature. In this article review, we will discuss the current trends in FND’s development, including comparison to the early development of quantum dots. We will also highlight some of the latest advances in fabrication, as well as demonstrations of their use in bioimaging and biosensing.

All-optical high resolution thermometry with color centers in diamond (Conference Presentation)

Living cells are likely to change their internal temperature during such natural processes as division, gene expression etc. Additionally, they actively react to environmental changes in temperature. Therefore, monitoring of intracell or near cell temperature opens the door for understanding intra-cell chemistry. However, most biological temperature changes expected be relatively small and transient, due to interactions with its environment. Hence, detecting this temperature change is quite challenging. We present the first systematic study of GeV spectra temperature shits on several different samples all demonstrating similar behavior. This temperature shits of zero-phonon line of GeV color center is powerful tool for precise all-optical detection of the temperature. Based on these studies we demonstrate all-optical thermometry with resolution well below 0.1K. Spatial resolution was demonstrated via implementation of the fiber based probe. Besides, we conducted series of proof of principal experiments in pillars and nanodiamonds this way proving possibility to measure temperature with submicron resolution. Achieved resolution together with chemical and physical inertness of nanodiamond passes the way for understanding of thermal function of living organisms and cells.