Inorganic Nanoparticle-Based Theranostics for Pulmonary Diseases

Pulmonary diseases, including tuberculosis (TB), chronic obstructive pulmonary disease (COPD), asthma, lung cancer, and pulmonary fibrosis, remain a leading cause of morbidity and mortality worldwide, and each presents a different combination of diagnostic and therapeutic problems. Theranostic nanoparticles, which carry diagnostic and therapeutic functions in a single construct, have been proposed as a way to address both at once. Inorganic nanoparticles are attractive for this purpose because their optical, magnetic, and structural properties are tunable and because their surfaces tolerate extensive modification. The term theranostic, however, is applied inconsistently: much of the literature described as theranostic reports particles characterized for imaging or for therapy, but not for both on the same construct. This review applies an explicit three-tier definition, distinguishing shared-mechanism platforms, integrated platforms whose diagnostic and therapeutic modes act independently, and single-function platforms with theranostic potential. We use it to assess gold nanoparticles (GNPs), silver nanoparticles (AgNPs), mesoporous silica nanoparticles (MSNs), superparamagnetic iron oxide nanoparticles (SPIONs), and quantum dots (QDs) in pulmonary disease. Attention is given to lung-specific constraints: the difference between inhaled and systemic administration, aerodynamic requirements for deposition, mucus and surfactant interactions, alveolar macrophage uptake, mucociliary clearance, and barriers that differ between fibrotic, infective, inflammatory, and malignant disease. We address limitations by material class rather than generically, because the dominant risk differs among silver ion release, gold persistence, iron-mediated redox chemistry, silica dissolution, and heavy metal leaching from QD cores. Several inorganic nanoparticle formulations have regulatory approval, but pulmonary theranostic applications remain preclinical, and we outline what would be required to change that.