## 4 Antibacterial Nanotheranostics
### Theranostic Nanoparticles (NPs) and Nanofibers
#### 4.1.3 Theranostic Electrospun Nanofibers  
Electrospinning is an economical, practical, and simple method for the preparation of nanofibers [180; 181; 182; 183]. The biological irony is that all human tissues and organs undergo deposition in nanofibrous forms (i.e., bone, dentin, collagen, cartilage, and skin) [184]. Electrospun nanofibers have intriguing properties stemming from (i) their nano-scaled cross-sectional dimensions, such as high surface areas consolidating their functionalization in a straightforward manner (e.g., drugs, ion-exchangers, nanostructures, and NPs), permeability, and porosity [185; 186; 187; 188; 189; 190]. (ii) Their macroscopic length facilitates a well-appreciatedease of manipulation [189]. These properties of electrospun nanofibers provide a valid account in biosensing [191; 192]. Biosensors could provide new vistas in wound care via detecting bacterial wound infections [193]. Electrospun fibers could be a winning strategy in wound dressing applications, hitting both goals of being physical barriers that prevent wound-associated infections and acting as a 3D scaffold that replaces the extracellular matrix (ECM) of the skin of the patient [181; 183; 185; 190]. Alteration in the well-orchestrated skin microbiota composition could be associated with the pathogenesis of inflammatory skin disease [194]. This is seen in chronic colonized wounds with a prolonged inflammatory phase, where bacteria produce inflammatory molecules, attracting inflammatory cells (i.e., neutrophils and macrophages) into the wound. Activated inflammatory cells secrete inflammatory cytokines, inducing the increased production of matrix metalloproteinases (MMPs). The high levels of MMPs degrade the ECM (a gel-like matrix secreted by the cells that it encloses and includes polysaccharides, water, and collagen proteins that elicit the unique elasticity, tensile strength, and compressibility of skin) and consequently impairs healing [139; 195]. _S. aureus_ is a scourge, commonly colonizing or secondarily infecting the skin of patients with atopic dermatitis [196] and producing delta-toxins that induce allergic immune and inflammatory skin disease [197]. Dermatologists are more inclined to prescribe topical corticosteroids and antibiotics for controlling atopic dermatitis. Phototherapy using ultraviolet (UV; UVA and UVB) is an effective way for controlling atopic dermatitis, especially with unresponsive patients to topical treatments [196]. In a study set out to determine the theranostic approach of fibers, [PERSON] et al. [198] used coaxial electrospinningning for preparing core-shell fibers for concurrent imaging and drug delivery. The shell was formed from Eudragit S100 (a pH-sensitive polymer), and the core was formed from poly(ethylene oxide) (PEO) loaded with both the magnetic resonance contrast agent (Gd(III) diethylenetriaminepentaacetate hydrate, Gd(DTPA)) and indomethacin (a non-steroidal anti-inflammatory drug). The cargoes (Gd(DTPA) and indomethacin) were not unloaded in the stomach because of the insolubility of the Eudragit shell in acidic pHs. In contrast, pH increases to alkaline in the intestine's terminal parts, dissolving the shell. The exposed PEO core to intestinal fluids would swell and adhere to the intestinal walls, unloading the Gd(DTPA) and indomethacin for concurrent imaging and treatment of inflammatory bowel disease, respectively. The pH-responsive drug-loaded electrospun nanofibers could further contribute to controlling implant- and wound-associated infections under the umbrella of nanotheransotics because pH differs in the physiological and pathological milies of the human body. For example, the acid-base homeostasis maintains the physiological pH of arterial blood in the range of 7.36 and 7.44 [199]. Physiologically, the skin has acidic pH, preventing bacterial colonization [200], whereas chronic wounds and highly infected wounds have alkaline pH (above 7.3).