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Register a new userNoncovalent force spectroscopy using wide-field optical and diamond-based magnetic imaging
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A realization of the force-induced remnant magnetization spectroscopy (FIRMS) technique of specific biomolecular binding is presented where detection is accomplished with wide-field optical and diamond-based magnetometry using an ensemble of nitrogen-vacancy (NV) color centers. The technique may be adapted for massively parallel screening of arrays of nanoscale samples.
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Sensitive, real-time optical magnetometry with nitrogen-vacancy centers in diamond relies on accurate imaging of small ($ll 10^{-2}$) fractional fluorescence changes across the diamond sample. We discuss the limitations on magnetic-field sensitivity resulting from the limited number of photoelectrons that a camera can record in a given time. Several types of camera sensors are analyzed and the smallest measurable magnetic-field change is estimated for each type. We show that most common sensors are of a limited use in such applications, while certain highly specific cameras allow to achieve nanotesla-level sensitivity in $1$~s of a combined exposure. Finally, we demonstrate the results obtained with a lock-in camera that pave the way for real-time, wide-field magnetometry at the nanotesla level and with micrometer resolution.
Wide field Raman imaging using the integral field spectroscopy approach was used as a fast, one shot imaging method for the simultaneous collection of all spectra composing a Raman image. For the suppression of autofluorescence and background signals such as room light, shifted excitation Raman difference spectroscopy (SERDS) was applied to remove background artifacts in Raman spectra. To reduce acquisition times in wide field SERDS imaging, we adapted the nod and shuffle technique from astrophysics and implemented it into a wide field SERDS imaging setup. In our adapted version, the nod corresponds to the change in excitation wavelength, whereas the shuffle corresponds to the shifting of charges up and down on a Charge-Coupled Device (CCD) chip synchronous to the change in excitation wavelength. We coupled this improved wide field SERDS imaging setup to diode lasers with 784.4/785.5 and 457.7/458.9 nm excitation and applied it to samples such as paracetamol and aspirin tablets, polystyrene and polymethyl methacrylate beads, as well as pork meat using multiple accumulations with acquisition times in the range of 50 to 200 ms. The results tackle two main challenges of SERDS imaging: gradual photobleaching changes the autofluorescence background, and multiple readouts of CCD detector prolong the acquisition time.
Multichannel imaging -- the ability to acquire images of an object through more than one imaging mode simultaneously -- has opened interesting new perspectives in areas ranging from astronomy to medicine. Visible optics and magnetic resonance imaging (MRI) offer complementary advantages of resolution, speed and depth of penetration, and as such would be attractive in combination. In this paper, we take first steps towards marrying together optical and MR imaging in a class of biocompatible particulate materials constructed out of diamond. The particles are endowed with a high density of quantum defects (Nitrogen Vacancy centers) that under optical excitation fluoresce brightly in the visible, but also concurrently electron spin polarize. This allows the hyperpolarization of lattice 13C nuclei to make the particles over three-orders of magnitude brighter than in conventional MRI. Dual-mode optical and MR imaging permits immediate access to improvements in resolution and signal-to-noise especially in scattering environments. We highlight additional benefits in background-free imaging, demonstrating lock-in suppression by factors of 2 and 5 in optical and MR domains respectively. Ultimate limits could approach as much as two orders of magnitude in each domain. Finally, leveraging the ability of optical and MR imaging to simultaneously probe Fourier-reciprocal domains (real and k-space), we elucidate the ability to employ hybrid sub-sampling in both conjugate spaces to vastly accelerate dual-image acquisition, by as much as two orders of magnitude in practically relevant sparse-imaging scenarios. This is accompanied by a reduction in optical power by the same factor. Our work suggests interesting possibilities for the simultaneous optical and low-field MR imaging of targeted diamond nanoparticles.
In microdosimetry, lineal energies y are calculated from energy depositions $epsilon$ inside the microdosimeter divided by the mean chord length, whose value is based on geometrical assumptions on both the detector and the radiation field. This work presents an innovative two-stages hybrid detector (HDM: hybrid detector for microdosimetry) composed by a Tissue Equivalent Proportional Counter (TEPC) and a silicon tracker made of 4 Low Gain Avalanche Diode (LGAD). This design provides a direct measurement of energy deposition in tissue as well as particles tracking with a submillimeter spatial resolution. The data collected by the detector allow to obtain the real track length traversed by each particle in the TEPC and thus estimates microdosimetry spectra without the mean chord length approximation. Using Geant4 toolkit, we investigated HDM performances in terms of detection and tracking efficiencies when placed in water and exposed to protons and carbon ions in the therapeutic energy range. The results indicate that the mean chord length approximation underestimate particles with short track, which often are characterized by a high energy deposition and thus can be biologically relevant. Tracking efficiency depends on the LGAD configurations: 34 strips sensors have a higher detection efficiency but lower spatial resolution than 71 strips sensors. Further studies will be performed both with Geant4 and experimentally to optimize the detector design on the bases of the radiation field of interest. The main purpose of HDM is to improve the assessment of the radiation biological effectiveness via microdosimetric measurements, exploiting a new definition of the lineal energy ($y_{T}$), defined as the energy deposition $epsilon$ inside the microdosimeter divided by the real track length of the particle.
Nitrogen-Vacancy centers in diamond possess an electronic spin resonance that strongly depends on temperature, which makes them efficient temperature sensor with a sensitivity down to a few mK/$sqrt{rm Hz}$. However, the high thermal conductivity of the host diamond may strongly damp any temperature variations, leading to invasive measurements when probing local temperature distributions. In view of determining possible and optimal configurations for diamond-based wide-field thermal imaging, we here investigate, both experimentally and numerically, the effect of the presence of diamond on microscale temperature distributions. Three geometrical configurations are studied: a bulk diamond substrate, a thin diamond layer bonded on quartz and diamond nanoparticles dispersed on quartz. We show that the use of bulk diamond substrates for thermal imaging is highly invasive, in the sense that it prevents any substantial temperature increase. Conversely, thin diamond layers partly solve this issue and could provide a possible alternative for microscale thermal imaging. Dispersions of diamond nanoparticles throughout the sample appear as the most relevant approach as they do not affect the temperature distribution, although NV centers in nanodiamonds yield lower temperature sensitivities compared to bulk diamond.
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