Quantum sensors that harness atomic defects within diamond as quantum bits have attracted much interest in application areas including photonics, quantum computing and biosensing. Of the hundreds of defects within diamond, the Nitrogen Vacancy (NV) defect is being widely studied due to the ability to optically address and read out its quantum spin state and its ability to sense magnetic fields, electric fields, temperature and chemical oxidation states at room temperature. In this talk, I will present results demonstrating the sensing capabilities of NV defects within diamond in biochemical solutions, mammalian cells, molecular cages and photomagnetic materials. Finally, I will discuss future prospects for sensitivity enhancement and miniaturisation leveraging photonic structures.
Fluorescent nano-diamonds (fND) containing negatively charged Nitrogen Vacancy (NV) centers have remarkable applications in biology such as bio-labelling and nanoscale sensing of cellular processes. The NV centers also act as atomic scale probes that are highly sensitive to the magnitude, direction and fluctuation of local magnetic fields. The work presented here reports on the development of a wide-field microscope using fNDs as biologically targeted quantum probes to monitor live cell dynamics associated with fluctuations in local magnetic and electric fields. fNDs were functionalized using antibodies to enable site specific targeting. Strategies were also implemented to overcome the formation of endosomes around fNDs once inside the cytoplasma, which not only inhibits targeting but also the resultant sensitivity to the cellular environment. In addition to fluorescent mapping, the exchange of magnetization between the magnetically active NV defects in the diamond lattice and paramagnetic species in the local environment was studied via acquisition of optically detected magnetic resonance spectra. The results of this work demonstrate the utility of fNDs as probes to monitor subcellular dynamics. The wide-field configuration of the microscope enabled fast acquisition of images essential to characterize transient events in live cells. Looking to the future, fNDs have tremendous potential to augment existing fluorescent probes and to enable magnetic resonance measurements on a nanoscale in live cell cultures.
In vivo bioluminescence imaging (BLI) has poor spatial resolution owing to strong light scattering by tissue, which also affects quantitative accuracy. This paper proposes a hybrid acousto-optic imaging platform that images bioluminescence modulated at ultrasound (US) frequency inside an optically scattering medium. This produces an US modulated light within the tissue that reduces the effects of light scattering and improves the spatial resolution. The system consists of a continuously excited 3.5 MHz US transducer applied to a tissue like phantom of known optical properties embedded with bio-or chemiluminescent sources that are used to mimic in vivo experiments. Scanning US over the turbid medium modulates the luminescent sources deep inside tissue at several US scan points. These modulated signals are recorded by a photomultiplier tube and lock-in detection to generate a 1D profile. Indeed, high frequency US enables small focal volume to improve spatial resolution, but this leads to lower signal-to-noise ratio. First experimental results show that US enables localization of a small luminescent source (around 2 mm wide) deep (∼20 mm) inside a tissue phantom having a scattering coefficient of 80 cm-1. Two sources separated by 10 mm could be resolved 20 mm inside a chicken breast.
Ultrasound modulated fluorescence tomography (USMFT) has the potential to be a useful technique to obtain fluorescence images with optical contrast and ultrasound (US) resolution in deep tissue. However, due to the intrinsic incoherent properties of fluorescence and the low modulation depth, the signal-to-noise ratio (SNR) and image contrast are poor. In this paper, the feasibility of using pyrene-labelled nanosize liposomes as contrast agents to improve the modulation depth in USMFT is investigated by using a light-scattering technique. Compared with microbubbles (MBs), which have been applied to USMFT to improve the modulation depth, liposomes are more stable and they can be manufactured with good repeatability. Also liposomes have a lower US scattering coefficient due to their liquid core as compared to the gas core of MBs, which can be advantageous when switching on fluorescence in a region of interest is required. Pyrene can form excimer fluorescence when in close proximity to other pyrene molecules. The exposure of these liposomes to US can change the collision rate of the pyrene molecules and hence modulate the optical emission. In the current work, 100 nm sized liposomes composed of varying concentrations of pyrene-labelled phospholipids were investigated to identify a suitable liposome-based US contrast agent candidate. The fluorescence emission of the pyrene-labelled liposomes insonified by continuous US were studied. It has been observed that the excimer emission from 0.5 mol% pyrene-labelled liposome is US sensitive at pressures between 1.4 MPa and 2.7 MPa. Possible fluorescence modulation mechanisms and application of pyrene-labelled liposomes for high-resolution, high-contrast fluorescence imaging are also discussed.
KEYWORDS: Signal detection, Modulation, Acoustics, Scattering, Signal to noise ratio, Reconstruction algorithms, Data modeling, Tissue optics, Ultrasonography, Transducers
In pulsed ultrasound modulated optical tomography (USMOT), an ultrasound (US) pulse performs as a scanning probe within the sample as it propagates, modulating the scattered light spatially distributed along its propagation axis. Detecting and processing the modulated signal can provide a 1-dimensional image along the US axis. A simple model is developed wherein the detected signal is modelled as a convolution of the US pulse and the properties (ultrasonic/optical) of the medium along the US axis. Based upon this model, a maximum likelihood (ML) method for image reconstruction is established. For the first time to our knowledge, the ML technique for an USMOT signal is investigated both theoretically and experimentally. The ML method inverts the data to retrieve the spatially varying properties of the sample along the US axis, and a signal proportional to the optical properties can be acquired. Simulated results show that the ML method can serve as a useful reconstruction tool for a pulsed USMOT signal even when the signal-to-noise ratio (SNR) is close to unity. Experimental data using 5 cm thick tissue phantoms (scattering coefficient μs = 6.5 cm−1, anisotropy factor g = 0.93) demonstrate that the axial resolution is 160 μm and the lateral resolution is 600 μm using a 10 MHz transducer.
Ultrasound imaging has benefited from non-linear approaches to improve image resolution and reduce the effects of
side-lobes. A system for performing second harmonic ultrasound modulated optical tomography is demonstrated which
incorporates both pulsed optical illumination and acoustic excitation. A pulse acoustic inversion scheme is employed
which allows the second harmonic ultrasound modulated optical signal to be obtained while still maintaining a short
pulse length of the acoustic excitation. For the experiments carried out the method demonstrates a reduction in the
effective line spread function from 4mm for the fundamental to 2.4mm for the second harmonic. The first use of pulsed
ultrasound modulated optical tomography in imaging fluorescent targets is also discussed. Simple experiments show that
by changing the length of the acoustic pulse the image contrast can be optimized. The modulation depth of the detected
signal is greatest when the length of the object along the acoustic axis is an odd number of half wavelengths and is
weakest when the object is an integer multiple of an acoustic wavelength. Preliminary ultrasound modulated imaging
results are also presented where the target generates light within the medium without the use of an external light source.
Although signal to noise ratio is likely to be a major challenge, this result highlights a potentially useful application of
ultrasound modulated optical tomography in bio- or chemi-luminescence imaging.
Tissue scaffolds are an integral part of the tissue engineering process, assisting in the culturing of cells in three
dimensions. It is important to understand both the properties of the scaffold and the growth of cells within the scaffold.
This paper describes a system to characterise scaffolds using acoustic techniques alone and the development of an
ultrasound modulated optical tomography system to study the growth of cells within the scaffolds.
Our interest is in characterising the properties of gel-based and polymer foam-based scaffolds. Results from a purely
acoustic system have been used to investigate the properties of foam scaffolds manufactured from synthetic polyesters
poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) via a supercritical fluid process. As these are porous
materials, they are particularly challenging acoustically as the pores scatter sound significantly. However, it is
demonstrated that acoustic signals are detectable through a 6mm thick scaffold.
Although acoustics alone can be used to characterize many properties of the scaffolds, useful information can also be
obtained from optical techniques e.g. monitoring the growth of cells within the scaffold via optical absorption or
fluorescence techniques. Light scattering is of course a significant problem for relatively thick engineered tissue
(~5mm). The acoustic approach has been extended to include laser illumination and detection of the ultrasound
modulated optical pulse. Images of optically-absorbing materials embedded in gel-based tissue phantoms will be
presented demonstrating that a lateral resolution of 250μm and an axial resolution of ~90μm can be achieved in
scattering samples.
In pulsed ultrasound modulated optical tomography (USMOT), as an ultrasound (U/S) pulse propagates, it performs as a
scanning probe within the sample, and modulates the scattered light spatially distributed along the axis of propagation.
By detecting and processing the modulated signal, the information along the U/S axis of the sample (1D image) is
studied. The signal is modelled as a convolution of the U/S pulse and the ultrasonic and optical properties of the medium
along the U/S focus. Based upon this model, a Maximum Likelihood (ML) method for image reconstruction is
established. The ML data inversion technique for a pulsed USMOT signal is, for the first time to our knowledge,
investigated both theoretically and practically. The ML method inverts the pulsed USMOT signal to retrieve the spatially
varying properties of the sample along the U/S scanning column, and then the optical absorption property can be
acquired. The results show that the ML method can serve as a useful fitting tool for a pulsed USMOT signal even in the
presence of noise. The work illustrates the application of this iterative algorithm on simulated and experimental data.
Experimental results using 5cm thick animal tissue phantoms (scattering coefficient μs is 6.5cm-1) demonstrate that the
resolution is better than 100μm using a 10MHz transducer.
To ensure the sustainability of tissue engineered products there is a need to consider the engineering and manufacturing
issues related to them particularly for the purposes of process optimization and product quality assurance. This work
describes the application of Raman spectroscopy for in process monitoring of a skin substitute and rotating orthogonal
polarization imaging to track collagen alignment in a tissue engineered tendon. The skin substitute studied is produced
from culturing fibroblasts in a fibrin matrix. Throughout the production process the fibroblasts secrete extracellular
matrix and in doing so deposit collagen in the matrix. Key to optimization of the skin substitute production process is
development of strategies to track the collagen and fibrin content. The work presented here discusses the feasibility of
Raman spectroscopy to resolve fibrin and collagen components in the skin substitutes. Collagen alignment is also
important in the engineering of many tissues, in particular tendons. Thus, this work will also investigate the ability of
rotating orthogonal polarization imaging to track collagen alignment in a tissue engineered tendon.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.