## 4 Conclusions  
Multi-arm amphiphilic block copolymers were prepared, and their micelles were used to encapsulate PtTFPP to enable the use of PtTFPP for oxygen sensing in biological conditions. The micelles prepared by using these block copolymers were around 40 to 200 nm, depending on the molar ratios of the hydrophobic and hydrophilic segments in the block copolymers. The micelles showed high storage stability. The PtTFPP encapsulated by micelle shows reasonable high quantum yields which are from 0.06 to 0.159. The micelles' response time is 20-30 s from deoxygenated solutions to oxygenated solutions, showing a rapid response to changes of dissolved oxygen concentrations. These new micellar biosensors were capable of in situ monitoring dissolved oxygen and oxygen consumption of _E. coli_ and living cells. The sensors were further demonstrated to be useful for drug screening through differentiating the influence of drug doses and species (antimycin A and ampicillin as two representative examples) on cells' metabolic activity. Since the sensor is in liquid form, it is easily used in many general commercial instruments, such as plate readers, and can be used for further biological understanding, disease diagnosis, and metabolic investigation. In this article, we introduce a novel multi-arm amphiphilic oxygen-sensitive probe for real-time measurement of dissolved oxygen concentration in extracellular or aqueous solutions. Compared with previous studies [27], ring-opening polymerization has the advantages of simple operation, high yield, and low cost. Furthermore, unlike linear polymers, multi-arm PEG that has higher terminal group concentrations than conventional linear polymers [35] is used, which enables the further modification or functionalization of the multi-arm polymers. Besides, this sensor shows excellent biocompatibility  
Figure 12: Inhibition of oxygen consumption monitored using micelle **M2** by ampicillin (**A**) and antimycin A (**B**) as typical antibiotics. The initial concentration of _E. coli_ is \(2\times 10^{6}\) cfu/mL. Experiments were carried out with mineral oil sealing. and faster response time for both cell and bacterial respiration measurements, indicating a good prospect in the biological field. The following are available online at [[http://www.mdpi.com/2076-3417/9/20/4404/s1](http://www.mdpi.com/2076-3417/9/20/4404/s1)]([http://www.mdpi.com/2076-3417/9/20/4404/s1](http://www.mdpi.com/2076-3417/9/20/4404/s1)), Figure S1: Stability of M1-M3 at 4 \({}^{\circ}\)C with PtTFPP determined by size changes, Figure S2: Critical Micelle Concentrations (CMC) of the polymers **P1** (**A**), **P2** (**B**), and **P3** (**C**), Figure S3: Oxygen consumption of _E. coli_ JM109 monitored with micelles **M1-M3** without oil sealing. Concentrations of PtTFPP were 3 ug/mL in each micelle. (**A**,**C**,**E**): Representative phosphorescence intensities' changes at 650 nm with _E. coli._ (**B**,**D**,**F**): Relative dissolved oxygen concentration changes with _E. coli._ (**A**,**B**) are for **M1**; (**C**,**D**) are for **M2**; (**E**,**F**) are for **M3**. Conceptualization, Y.T., F.S. and Y.Q. ; methodology, Y.Q. and T.P. ; Validation, Y.Q. and J.L. ; Formal analysis, Y.Q. and T.P. ; Investigation, Y.Q., J.L., J.W. and C.Y. ; Resources, S.W., Y.T. and F.S. ; data curation, Y.Q., K.Z. and T.P. ; writing-original draft preparation, Y.T. and Y.Q. ; writing-review and editing, Y.T., F.S. and Y.Q. ; visualization, Y.Q. ; supervision, S.W. and Y.T. ; project administration, Y.T. This research was funded by National Natural Science Foundation of China (21574061, 21604036, 21774054), Shenzhen fundamental research programs (JCYJ20170412152922553), the start-up fund of SUSTech (Y01256114), and Student's Platform for Innovation and Entrepreneurship Training Program (Grant No. 2018S11).