Multiplexed Detection Applications
Detection capability of the optofluidic chips is characterized by flowing just buffer and then fluorescent test beads of a standard size (200nm) through the chip. The fluorescent signals from the beads are send to an avalanche photo detector through the chips collection waveguide. The fluorescent tests are done for different wavelengths based on application (such as 488nm and 633nm). The background noise of the chip is determined from the test signals of the buffer and SNR is quantified from test signals of the beads.
Single mode and multi mode waveguides are tested separately. Zooming into single events show the single peak event from the bead excited by the SM waveguide and multi peak signal from multi mode waveguide. Peak counting algorithms or analysis of the auto-correlation of the signals can be used to distinguish signals from different fluorescent color labeled targets. Other signal processing algorithms are also used to distinguish targets combinatorialy labeled with more than one color.
7X Spectral Multiplexing:
An example here shows 7 different targets (Synthetic DNA strands corresponding to antibiotic-resistant mutations) combinatorial labeld with D.Red, Red and Green fluorophores. The chip is excited with all three lasers (738nm, 633nm, 556nm) simultaneously. Signal from each target has the information of its color tags embedded in it via the distinct MMI patterns that excite them. A signal processing algorithm helps us automatically decode the spectral information in the signals and thus identify the targets.
3X Spacial Multiplexing:
Multiplexed detection of three antibiotic resistant bacterial plasmids (KPC, NDM, VIM) is also demonstrated with single molecule sensitivity. Here spacial multiplexing (Spectral multiplexing was used in the previous example) is used via dedicated fluidic line for each plasmid. A sinlge MMI waveguide intersects the three fluidic line and are designed to generate distinct excitation pattern in each channel. Signal from each fluidic line is collected and send to a single detector using 3x1 Y coupler collection waveguides. Thus 3x multiplexing can be done with a single laser source.
