**5. Assembly of cell-based periodical structures by OFTs**

In addition to the assembly of biophotonic waveguides with one type of cells, assembly of periodical structures of different types of cells was also demonstrated using OFTs [19]. Using *E. coli* cells and *Chlorella* cells as examples, different cells are flexibly patterned into one-dimensional (1D) periodic cell structures with controllable configurations and lengths (**Figure 6**), by periodically connecting one type of cells with another by optical force. Further demonstration shows that the structures show good performance for light propagation and can be moved flexibly. Real-time light signals can be detected from these photonic structures. These features make these photonic structures excellent candidates for the detection of signals transducing among different patterned cells. This assembly and patterning technique can also be applicable for other cells, such as mammalian cells and human cells.

#### **Figure 6.**

*Experimental schemes for cell assembly into periodical structures [19]. (a) an OTF is placed in cell suspensions. (b) Laser launched, multiple E. coli cells trapped. (c) a Chlorella cell is trapped and connected to the former trapped E. coli cells. (d) a periodical structure is formed, and light propagates along the periodical structure. (e) Schematic shows the assembled periodical biophotonic structures.*
