695nm Bandpass Filter

Context: A fluorescence-based biosensing platform designed to detect specific biological targets (like DNA or proteins) using molecular beacons or FRET (Fluorescence Resonance Energy Transfer) pairs.

Usage of Filter: The 695 nm bandpass filter is used as an optical emission filter in the detection path, specifically paired with a 532 nm excitation laser.

Function: Its primary function is to block the intense 532 nm laser light (excitation source) and any background autofluorescence while selectively transmitting the deep-red fluorescence emitted by the target fluorophore (e.g., an acceptor dye in a FRET pair that emits near 695 nm).

Result: It achieves a high signal-to-noise ratio, allowing the system to accurately quantify the presence of macromolecules based on the specific fluorescence intensity, effectively distinguishing the "signal" (bound target) from the "noise" (excitation light).

Context: Flow cytometry and high-throughput cellular analysis systems used to identify and sort cells based on surface markers or viability.

Usage of Filter: The 695 nm bandpass filter (commonly specified as 695/40 nm) is used as a fluorescence collection filter for a specific channel (often the FL3 channel in standard configurations).

Function: It isolates the emission spectrum of specific long-wavelength fluorophores, most notably PerCP-Cy5.5 (Peridinin Chlorophyll Protein-Cyanine 5.5). It separates this signal from shorter wavelength emissions like FITC (green) or PE (orange) and blocks the 488 nm excitation laser.

Result: It enables multicolor analysis, allowing researchers to simultaneously measure multiple characteristics of a single cell (e.g., identifying a T-cell subset while simultaneously checking for cell viability) without signal "crosstalk" between the different dyes.