Direct Detect^® Infrared Spectrometer for Total Protein Quantitation

How to use infrared spectroscopy to measure total protein concentration consistently (from one experiment to the next) and without knowing the sequence of the protein(s) being measured

Accurately and consistently measuring the total protein concentration in a sample can generate more reliable immunoassays, more informative Western blots of lysates, and streamlined optimization of protein purification. Infrared spectroscopy is a long-standing, accepted method for accurate protein quantitation; however, traditionally, this technology required significant spectroscopy expertise and large instruments.

The Direct Detect system has made infrared spectroscopy accessible to any protein laboratory, benefiting researchers performing several protein quantitation procedures a week, and especially researchers who are dissatisfied with other quantitation methods, (such as UV-Vis spectroscopy, and Bradford, BCA, and Lowry assays).

The Direct Detect Method

After generating a single-time standard curve that gets stored in the instrument, just spot 2 μL of sample and triplicate and blank onto an assay-free membrane card and inserting it into the spectrometer. The system reports the average protein concentration of 3 spots and displays the IR spectrum of the sample.

Benefits of the Direct Detect Spectrometer

• By measuring amide bonds in protein chains, the system accurately determines an intrinsic component of every protein without relying on amino acid composition, dye-binding properties or reduction-oxidation (redox) potential.
• Minimal learning required, can be used without IR expertise
• Minimal to no sample preparation
• Preserves precious samples - requires only 2 μL per single analysis
• No assay involved (analysis based on chemical composition)
• System stores and reuses standard curves
• Generation of new calibration curve takes around 30 minutes

Video. Direct Detect Infrared Spectrometer helps one customer quantitate total protein
while saving sample

Figure 1. Measuring protein concentration without interference from SDS, thanks to nonoverlapping IR signals in the Direct Detect spectrometer.

Features of the Direct Detect Spectrometer

IR Spectrometer:

• Fourier-Transform Infrared (FT-IR) spectrometer
• Compact footprint (11 in x 8 in; 30 cm x 22 cm)
• Analysis range 500 – 6000 cm⁻¹
• Operates in transmission mode analyzing dried sample
• Fan incorporated into the sample chamber helps to dry the sample spot
• Internal humidity sensor controls analysis conditions
• Intuitive assay and analysis software

Assay-free Sample Card:

• Disposable, 4-position sample carrier
• Easy, single-step sample application
• Reliable sample containment
• Consistent presentation of sample in the center of the spot for interrogation by the MIR beam
• Direct analysis (no reaction or chemical modification needed)