Research On Bacterial Inhibition And Imaging Applications Based On Photo-active Materials

In natural state,humans coexist with multiple types of bacteria,including symbiotic bacteria that maintain the balance of their organism,and pathogenic bacteria that break the organism balance and induce disease.Light as a trigger source has remote controllability,high spatial and temporal resolution,and biosafety,which allows it to manage and intervene strain.Development of microbial management solutions based on light-triggered materials,can more precisely understand and even change the status of microorganisms,including tracing/regulating symbiotic bacteria,or tracing,diagnosing,inhibiting/regulating pathogenic bacteria,etc,which is in line with the trend of precision medicine and is important for the balance of living organisms,including metabolic balance,hormonal balance,and immune barrier.Based on the great prospect of light manipulated nanomaterials for bacteria management.Our research is as follows:（1）Faced with the infectious wounds problem caused by pathogenic bacteria,we develop infected wound healing strategies based on light-triggered means.Photothermal therapy（PTT）hydrogel dressings hydrogels were prepared based on tannic acid-Fe³⁺nano-self-assemblies（TFe）,which were the source of the photothermal efficiency.TFe,with facile preparation and biocompatibility,are compounded with the sodium alginate-Ca²⁺-chitosan（SC）by electrostatic adsorption and ionic ligand cross-linking to form a composite hydrogel dressing（TFe@SC）,which is suitable for large area preparation.However,it was found that Fe³⁺and catechols structure in TFe have competition for the ionic coordination between sodium alginate-Ca²⁺of the hydrogel skeleton,which affects the formation of the hydrogel structure.In this regard,we have made a careful discussion to explore the optimal ratio of each component for construction of the TFe@SC hydrogel with high photothermal conversion efficiency.Under 808 nm light excitation,the dressing warms up above 60°C,which promote bacterial apoptosis and thereby facilitating infected wound healing in mice.（2）Based on the SC hydrogel with ease of preparation and excellent biocompatibility,zinc porphyrin nano self-assemblies（Zn Tcpp）were further introduced within the SC structure to prepare Zn Tcpp@SC composite hydrogels for wound bacterial inhibition.The antibacterial properties mainly rely on the production of singlet oxygen by Zn Tcpp under photoactivation,which requires Zn Tcpp close contacts with bacteria for further inhibition.Therefore,it is important that Zn Tcpp@SC hydrogel dressing adsorbs bacteria,or that Zn Tcpp nanomaterials adhering to the surface of bacteria.Compared with the effect of TFe on the structural formation of hydrogel dressings in work one,Zn Tcpp nanomaterials have no significant effect on the structural formation of Zn Tcpp@SC composite hydrogel,which greatly reduces the difficulty of dressing construction.Due to the weaker physical binding between Zn Tcpp nanomaterials and SC hydrogels,the Zn Tcpp@SC composite hydrogels controlled the release of Zn Tcpp nanomaterials in an infected wound p H（7.15-8.9）environment.The degree of controlled release was influenced by the formation parameters of Zn Tcpp@SC composite hydrogels.By tuning the parameters,composite hydrogels with slow release of Zn Tcpp nanomaterials were constructed.As tested by electron microscopy,the bacteria are adhered by the hydrogel and the hydrogel-controlled Zn Tcpp is enriched on the surface of the adhered bacteria.Under the excitation of 650 nm light,the composite hydrogel had significant antibacterial effect in the environment.（3）Accurate localization of probiotic distribution in the gut helps to understand the intrinsic mechanisms.Light-triggered bacterial imaging clearly reports the location of their distribution,with real-time,dynamics,and high imaging resolution.In contrast,conventional imaging probes for studying microorganisms in vivo generally suffer from low imaging penetration and poor resolution.Based on this,we developed a method to observe the distribution of orally transplanted bacteria in the intestine in a stable,dynamic,and highly spatial and temporal resolution.Firstly,EDC/NHS chemically activated the carboxyl groups on the surface of Lactobacillus bulgaricus,and then the lanthanide nanomaterials Na Gd F₄:Yb³⁺,Er³⁺@Na Gd F₄,Nd³⁺（Er@Nd）were further labeled on the surface of Lactobacillus bulgaricus.The nanomaterials have both Stokes and anti-Stokes luminescence properties and can emit both visible light and NIR-IIb（1500-1700 nm）light under 808 nm excitation,with the NIR-IIb region light being able to observe signals in living tissue with high spatial and temporal resolution.In Ga As NIR-II imaging equipment was used to capture NIR-IIb signals to monitor the distribution of transplanted bacteria in the living intestine,and combined with two-photon excitation（TPE）microscopy to capture visible light signals to further examine microbial labeling in intestinal tissues.This dual-technology synergistic approach to the study of probiotic distribution and labeling in the gut provides an innovative approach to the in-depth study of orally transplanted bacteria.