Conspectus
X-ray luminescence is an optical phenomenon
in which chemical compounds
known as scintillators can emit short-wavelength light upon the excitation
of X-ray photons. Since X-rays exhibit well-recognized advantages
of deep penetration toward tissues and a minimal autofluorescence
background in biological samples, X-ray luminescence has been increasingly
becoming a promising optical tool for tackling the challenges in the
fields of imaging, biosensing, and theragnostics. In recent years,
the emergence of nanocrystal scintillators have further expanded the
application scenarios of X-ray luminescence, such as high-resolution
X-ray imaging, autofluorescence-free detection of biomarkers, and
noninvasive phototherapy in deep tissues. Meanwhile, X-ray luminescence
holds great promise in breaking the depth dependency of deep-seated
lesion treatment and achieving synergistic radiotherapy with phototherapy.
In this Account, we provide an overview of recent advances in developing
advanced X-ray luminescence for applications in imaging, biosensing,
theragnostics, and optogenetics neuromodulation. We first introduce
solution-processed lead halide all-inorganic perovskite nanocrystal
scintillators that are able to convert X-ray photons to multicolor
X-ray luminescence. We have developed a perovskite nanoscintillator-based
X-ray detector for high-resolution X-ray imaging of the internal structure
of electronic circuits and biological samples. We further advanced
the development of flexible X-ray luminescence imaging using solution-processable
lanthanide-doped nanoscintillators featuring long-lived X-ray luminescence
to image three-dimensional irregularly shaped objects. We also outline
the general principles of high-contrast in vivo X-ray
luminescence imaging which combines nanoscintillators with functional
biomolecules such as aptamers, peptides, and antibodies. High-quality
X-ray luminescence nanoprobes were engineered to achieve the high-sensitivity
detection of various biomarkers, which enabled the avoidance of interference
from the biological matrix autofluorescence and photon scattering.
By marrying X-ray luminescence probes with stimuli-responsive materials,
multifunctional theragnostic nanosystems were constructed for on-demand
synergistic gas radiotherapy with excellent therapeutic effects. By
taking advantage of the capability of X-rays to penetrate the skull,
we also demonstrated the development of controllable, wireless optogenetic
neuromodulation using X-ray luminescence probes while obviating damage
from traditional optical fibers. Furthermore, we discussed in detail
some challenges and future development of X-ray luminescence in terms
of scintillator synthesis and surface modification, mechanism studies,
and their other potential applications to provide useful guidance
for further advancing the development of X-ray luminescence.