# A Photolysis-Assist Molecular Communication for Tumor Biosensing
## 2 System Model  
### Biosensing for Tumor  
In the presence of a tumor, several biological properties changes have been observed in the microenvironment of the peritumoral region, which includes fluctuations in blood velocity [16], changes in oxygen levels [17], temperature variations, reshaping of the fibrosis vasculature [18], and alterations in pH profile [5]. In [19], [PERSON] et al. report Several brain-tumor-derived biomarkers accumulate in the blood or cerebrospinal fluid, including nucleic acids, proteins, small molecules, such as H\({}_{2}\)O\({}_{2}\)[20], specific amino acids [21], and extracellular vesicles.  
Dissemination of tumor cells is a vital step in tumor metastasis [22]. Thus, the real-time dissemination signals directly correlated with metastasis are indisputable evidence for tumor biosensing. Therefore, as reported in [22], using intravalicroscopic imaging (IVM), [PERSON] et al. found that transient vascular permeability and tumor cell intravasation occur simultaneously and exclusively in the tumor microenvironment of metastasis ( TMEM). Furthermore, with the advancements in bioluminescence imaging and bioluminescence reporters in IVM, [PERSON] et al. [23] demonstrated that it is capable of imaging signalling dynamics in real time in the TMEM. The rapid proliferation of tumor cells causes an insufficient supply of blood, which results in a lack of oxygen and other nutrients. As a result, cancer cells produce lactic acid, which contributes to a lower pH in tumors than in normal tissue (pH = 7.4) [5]. Consequently, these pH-responsive and real-time changes in TMEM require a high transmission rate to deliver the information for biosensing.  
Such real-time changes in conditions of the microenvironment could be regarded as time-variant biological gradients induced by specific tumor. It is essential to sense the information towards the biological gradients for tumor detection. Nanoparticles can be designed to respond to pH by changing surface chemistry, changing particle size or shape, disassembling or releasing cargo in [24]. The last few years have seen many breakthroughs concerning finding pH-responsive nanoparticles with extremely low toxicity toward healthy cells [25]. For instance, self-assembled micelles [26], which are stable at a physiological pH of 7.4, swell in acidic environments, such as intracellular (pH = 6.8) and endosomal (pH = 5.5). Moreover, as indicated in the review [24], synthesizing pH-responsive nanoparticles has attracted significant interest in drug delivery systems since nanoparticles could be internalized into cells via acidified vesicles. Meanwhile, the result also demonstrated that pH-responsive polymer polymer-modified nanoparticles could enhance drug loading and release rate of the anticancer drug 5-fluorouracil as reported in [27]. In [28], [PERSON] et al. realise the AND, OR, NAND, NOR, XOR, and XNOR gates by the manufactured NP-OG constructs, which conjugates the pH-responsive Oregon Green 488 (OG) to the nanoparticles with a trypsin-cleavable peptide. The constructs allow for efficient fluorescent biosensing with logic gates [28]. In [29], the DNA-grafted hemin was utilized not only as of the module for dynamic DNA assembly but also as the tunable mimetic enzyme; then, activated hemin-mimetic enzymes can provide a simple, fast and signal amplification strategy for fluorescent biosensing. To facility the target-triggered DNA self-assembly catalytic system, the fluorescent spectra can be generated [29]. We follow this work, adopted as a component in the receiver, in which the specific molecules trigger fluorescent generation. The pH conditions detected by pH-responsive NP-OG constructs could be coded as the information to be transmitted.