The inherently interdisciplinary nature of developing instrumentation for life sciences requires a high level of collaboration between scientists and engineers across the fields of analytical or clinical chemistry, optics, mechanics, material science, and microbiology. Moreover, product development teams are competing for first-tomarket benefits that are driven by intellectual property lifetimes and insuring an installed base quickly to realize recurring consumable sales. Concurrently, product designers need to comply with current Good Manufacturing Practices (cGMP). System-level modeling enables adherence to the methodical design process without the cost and time associated with iterative hardware prototyping and laboratory and clinical testing.

Fluorophore Beginnings

Figure 1: Basic spectrofluorometer system layout.
A Design-for-Manufacture (DFM) process recently was executed for a fluorescence spectroscopy product platform (see Figure 1). A multi-disciplinary design team eliminated the cost of quality using a formal design method, facilitated by Lambda Research Corporation’s TracePro suite of 3D opto-mechanical design tools and SolidWorks’ (Concord, MA) 3D mechanical design software.

Figure 2: TracePro Bridge allows optical component properties to be permanently stored and translated into SolidWorks design files, improving design simulation, documentation, and time to market.
Like many life science systems, spectrofluorometer platform development presents rigorous design challenges, including identifying optical layout and fluorophore alternatives, minimizing the exponential cumulative effect of component quality and quantity, tolerancing component dimensions, and complying with GMP documentation and traceability requirements. The design is highly constrained in terms of cost and the requirement to achieve both the sensitivity and dynamic range to detect the presence of a breadth of fluorescence-tagged proteins.

Based on the target protein, platform development began with the selection of fluorescent dye, Alexa Fluor 488. The dye was chosen because it has the proper reactive groups and accommodates assay conditions including photostability and pH. Optical properties of the dye, including relative excitation and emission curves and the peak molar extinction coefficient, are retrieved from the Invitrogen Molecular Probe Products database resident in TracePro and TracePro Bridge for SolidWorks.

The dye was modeled in an aqueous solution with a pH>8. Quantum efficiency was determined by biochemists to be 0.92 as a free dye and 0.55 when conjugated to the target protein. The initial design tests the feasibility of the fluorophore concentration at 10 E -10 moles per liter. A range of concentrations is modeled to validate adherence to the dynamic range specification.

Source and Detector Models

Based on the peak excitation wavelength of Alexa Fluor 488 dye, an excitation source is selected that balances a wavelength closest to peak excitation, luminous flux, and cost. A blue LED, Kingbright (City of Industry, CA) model WP7524PBC/J, with wavelength of 467 nm, ±22 nm, was selected and its SolidWorks model and optical properties were downloaded from the Kingbright Web site and imported into the TracePro model. Luminous flux and directionality of the LED’s output were characterized in lab and imported into the TracePro model.

Based on the peak emission wavelength of the Alexa Fluor 488 dye (517 nm), a detector was selected that balanced cost and responsivity. A silicon photodiode was selected and its spectral responsivity curve was imported into the TracePro model (see Figure 2).

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