# M13 Bacteriophage-Assisted Synergistic Optical Enhancement of Perovskite Quantum Dots
## 3 Results and Discussion  
### Morphology and Optical Characterizations of CsPbI\({}_{3}\) QDs with the M13 Phage  
We first examined the photoluminescence of PQDs coupled with the M13 phage in solution for different concentrations. Different concentrations of the M13 phage (0.1 mg/mL, 0.25 mg/mL, 0.5 mg/mL, 0.75 mg/mL, and 1 mg/mL) are utilized when mixing with PQDs (fixed = 1 mg/mL). By varying different concentrations of the M13 phage, it is possible to investigate its role in estimating the photoluminescence properties of the perovskite quantum dots. By increasing or decreasing the concentration, we can observe any changes in the intensity or resonance wavelength. For reference, the absorbance spectrum of the M13 phage has also been measured, as shown in supporting information Figure S1. Theresults indicate no significant influence in the visible region. Because the M13 phage is composed of proteins, only the scattering effect is expected in the visible region.  
The elongated structure allows for the binding of multiple PQDs along its length, effectively increasing its density on the nanofibrous M13 phage. The fabrication of the hybrid structure was performed using a simple technique shown in Figure 1b. The transmission electron microscope (TEM) image of CsPbI3 PQDs reveals tiny cubic nanocrystals with sizes ranging from 15 to 16 nm (Figure 1c). This simple technique allowed for the binding sites on the phage surface to interact with the quantum dots, promoting their self-assembly within the nanowire. As the two solutions were combined, the concentration of the PQDs on the M13 phage(s) increased, resulting in a highly organized and densely packed arrangement (see supporting information Figure S2). Figure 1d shows the absorption spectra of CsPbI3 PQDs with an absorption edge at 653 nm and a strong PL emission at 675 nm under 405 nm excitation. The full width at half maximum (FWHM) of the PL band is as narrow as 34 nm.  
The absorption of PQDs with different M13 phage concentrations are shown in Figure 1e, which exhibits increased absorption in the longer wavelength part compared to that of pure PQDs. This enhanced absorption, particularly in the long wavelength region, can be attributed to the presence of the M13 phage(s), which acts as a scaffold for the quantum dots, allowing for their efficient incorporation into the nanowire structure [48; 57]. The proximity and alignment of the PQDs within the nanofibrous structure facilitate efficient energy transfer and enhance photon absorption in the longer wavelength region. This is attributed to the strong interaction between the M13 phage scaffold and the PQDs, enabling optimal positioning and alignment of the quantum dots within the nanowire matrix.  
Figure 1f displays photographs of PQD + M13 phage solutions under normal light, with the index number showing the concentration of the M13 phage in mg/mL. The results demonstrated that varying concentrations of the M13 phage led to distinct colors and transparency levels in the solution, with the highest concentration showing a transparent appearance. We assume that the higher concentrations of the M13 phage may cause stronger absorption and scattering effects, influencing the transmission of light through the mixture, and consequently altering the transparency levels. The study also observed a slight difference in appearance between the pure PQDs solution and PQDs mixed with the M13 phage, including the presence of bubbles in the M13 phage solution.