# Research Progress of Polysaccharide-Gold Nanocomplexes in Drug Delivery
## 6 Drug Release from Polysaccharide-AuNPs  
In recent years, there has been a significant increase in the attention given by researchers to responsive nano-drug release systems. This is primarily due to these systems' unique triggering response mechanism. The primary purpose of these systems is to deliver drugs with precision to the tumor site, ensuring that treatment can be given on demand. By doing so, the occurrence of serious side effects resulting from early drug leakage and off-target drug delivery can be minimized. One of the driving factors behind the development of these systems is the recognition that the microenvironment at the site of infection differs from that of normal tissue. Specifically, there are differences in terms of substance concentration and composition. As a result, researchers have focused their efforts on creating responsive nano-drug release systems that both internal and external stimuli can trigger. Internal stimuli include pH and enzymes, while external stimuli include photothermal, laser-to-light, and ultrasound signals. Furthermore, researchers have also explored intelligent targeting methods that enable tumor-specific identification and targeted drug release. These advancements have significantly contributed to the responsive nano-drug release systems field. As a result, there is great promise for improved drug delivery in the future (Figure 7) [139]. Under the irradiation of light at specific wavelengths, the surface of gold nanoparticles generates the phenomenon of LSPR (Figure 7A), which gives the gold nanoparticles high photothermal conversion efficiency for use as photothermal and photosensitizer carriers [140]. Phototherapies, evolving rapidly as cancer treatment modalities, utilize light of different wavelengths to induce photochemical or photothermal changes within specific tissues [141]. Two commonly used forms of phototherapy are photodynamic therapy (PDT) and PTT. Both treatments involve the use of light and either exogenous or endogenous absorbers. These therapies aim to produce cytotoxic ROS or raise the local temperature in a targeted manner [142]. PDT and PTT techniques offer a significantly higher level of spatiotemporal control when compared to systemic therapies. This leads to a reduction in off-target toxicities. Simultaneous PTT and PDT cancer therapy is accomplished by leveraging the gold nanoparticle's thermal properties and its role as a drug delivery carrier for transporting the photosensitizer (PS) [140]. [PERSON], [PERSON] et al. prepared a novel nanoplatform system consisting of porphyrin derivatives and Au NPs, in which modified chitosan was encapsulated on the surface of Au NPs through ligand exchange between sulfhydryl groups and Au. The chitosan-coated Au NPs (QCS-SH/Au NPs) were further coupled with endo-tetrakis(4-sulfophenyl)porphyrin (TPPS) to obtain porphyrin-conjugated Au-hybridized nanoparticles (TPPS/QCS-SH/Au NPs) Figure 7B briefly describes the preparation of TPPS/QCS-SH/Au NPs and their anticancer properties via PDT/PTT [143]. Notably, it has been observed that AuNPs functionalized with polysaccharides exhibit markedly improved effects in both PTT and PDT when compared to bare gold nanoparticles. This significant finding highlights the compelling potential for the application of polysaccharide-functionalized AuNPs in tumor therapy [143]. In recent years, PTT based on NIR light irradiation (in the wavelength range of 650-1400 nm) has gained widespread use due to its unique advantages. One of the main advantages is the excellent tissue penetration and minimal damage to healthy tissue it demonstrates. Specifically, NIR light is effective in penetrating the head of newborns to a depth of several millimeters [144; 145]. Among various photothermal materials, gold nanostructures have gained significant attention in the field of PTT due to their remarkable LSPR properties. These properties are primarily responsible for inducing a photothermal effect.