X‐Ray Excited Luminescence Chemical Imaging of Bacterial Growth on Surfaces Implanted in Tissue

Abstract

We develop a pH sensor film that can be coated on an implant surface and imaged using a combination of X-ray excitation and visible spectroscopy to monitor bacterial infection and treatment of implanted medical devices (IMDs) through tissue. X-ray scintillators in the pH sensor film generate light when an X-ray beam irradiates them. This light first passes through a layer containing pH indicator that alters the spectrum according to pH, then passes through tissue where it is detected by a spectrometer. A reference region on the film is used to account for spectral distortion from wavelength-dependent absorption and scattering in the tissue. pH images are acquired by moving the sample relative to the X-ray beam and collecting a spectrum at each location, with a spatial resolution limited by the X-ray beam width. Using this X-ray excited luminescence chemical imaging (XELCI) to map pH through porcine tissue, we detected a pH drop during normal bacterial growth on the sensor surface, and a restoration of the pH to the bulk value during antibiotic treatment over the course of hours with millimeter resolution. Overall, XELCI provides a novel approach to noninvasively image surface pH for studying implant infections and treatments.

Bright Lu2O3:Eu Thin‐Film Scintillators for High‐Resolution Radioluminescence Microscopy

“…Similar to other scintillator-based imaging techniques, [18] radioluminescence microscopy uses scintillator properties to study biological processes on a physical scale not previously possible. Our results indicate that the spatial resolution of radioluminescence spectroscopy is dramatically impacted by the properties of the scintillator used.…”

X-ray excited luminescent chemical imaging (XELCI) for non-invasive imaging of implant infections

“…The resolution of the system is limited to the size of the x-ray beam that excites the particles as well as the thickness of the scintillator and pH sensor films, and the thickness of any opaque well targets. In previous studies, we showed that submillimeter knife-edge resolution is acquired with submillimeter X-ray beams 15, 16 , and that the resolution can be reduced by using a larger collimated beam 13 . Here an IFG iMOXS/1-MFR X-ray source (Fischer Technology Inc, Windsor, CT) was used with a slightly focusing polycapillary X-ray optic and a 51 mm working distance.…”

“…In this case, the scintillator is Gd2O2S:Eu, which emits light at 620 nm and 700 nm, and the light modulator is bromocresol green, a pH-sensitive film, which absorbs more 620 nm light at high pH, than at low pH; the 700 nm peak is minimally absorbed regardless of pH, and serves as a spectral reference signal. 13 Above the pH sensitive film is tissue which ranges in thickness depending on the site of implantation. In order to image these sensors, sample (or an x-ray and collection optics) are mounted to an x-y linear stage which causes the x-ray spot to scan across the sensor while pH measurements are acquired at each point.…”

“…The XELCI was acquired with the sensor sandwiched between two 6 mm thick slices of chicken breast tissue. The method generated high resolution surface-specific pH images, but the images were very slow to acquire because each spectrum was acquired on a microscope spectrometer as the microscope stage was moved 13 . We also demonstrated a similar time-dependent surface pH measurement using 980 nm excitation of upconversion luminescence, however, spatial resolution is limited by diffuse optical scattering of the excitation beam which has a point spread function fwhm about the tissue depth being imaged through 14 .…”

Implanted chemical sensors for functional radiography

“…25,26 The environment adjacent to an infected implant surface is reportedly in the range of pH 4 -6 depending on location and other factors. [27][28][29] These acidic regions play a critical role in biofilm resistance to antimicrobials because low pH affects antibiotic chemistry, host innate immune response, and bacterial metabolism. 30 According to the literature, low pH can be expected during the normal inflammatory phase of necrosis and hematoma formation post-surgery, with sustained acidosis seen with infection or severe chronic inflammation and a return to physiological pH with normal healing.…”