Streptavidin Conjugation Protocol

CPNs™ can be readily conjugated to proteins using EDC (N-ethyl-N’-dimethylaminopropyl-carbodiimide), which enables linkage of the protein amine groups (-NH2) to the carboxyl groups on the surface of the CPNs™ (-COOH). Attaching proteins such as antibodies or streptavidin (to enable biotinylated linkage) will create highly selective fluorescent probes, which can target specific molecules of interest. The immense brightness of CPNs™ allows detection of molecules with a high degree of sensitivity. Single molecules can be detected using a wide variety of applications, including flow cytometry, immunocytochemistry and histochemistry methods, and ELISA.

The affinity of targeting molecules varies greatly and an initial titration for the CPNs™:targeting molecule ratio must be undertaken. Similarly, final usage dilution of the CPNs™ in the targeting molecule conjugate will need to be determined empirically.


  1. Add 50 μl CPN™ (0.1mg/ml) to 870 μl of water
  2. Add 20 μl of HEPES 1M
  3. Add 20 μl PEG 8000 5% w/v
  4. Add 40 μl streptavidin (1mg/ml) and vortex (several ratios of CPN™:targeting molecule should be tested to identify the optimum conditions, e.g. 10-100 μl targeting molecule (1mg/ml))
  5. Add 20 μl freshly prepared EDC solution 5 mg/ml
  6. Shake mixture for 4 hours at room temperature
  7. Add 20 μl BSA (10% w/v) and leave to shake for a further 30 minutes
  8. The CPN™:streptavidin conjugates can then be purified from the reaction components by precipitating them using a magnet
  9. Re-suspend in 40 μl PBS: The linked protein may make the suspension susceptible to microbial contamination. It is recommended that 3.2 mM (0.02%) sodium azide (or alternative antimicrobial) is added and stored at 4 °C.


  • HEPES (1M), pH 7.4
  • PEG 8000 (5% w/v)
  • Streptavidin (1 mg/ml)
  • EDC [N-(3-Dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride] 5 mg/ml (Freshly make EDC solution and use immediately. Discard any unused.)
  • Bovine Serum Albumin (10% w/v), pH 7.4
  • Phosphate buffered saline


CPNs™ can be used in a variety of in vitro imaging applications to maximise the success of your R&D.


CPNs™ boast superior optical, biological and structural properties to market equivalents

Why so bright?

Our CPN™ products retain their fluorescence much longer than existing technologies, whilst remaining chemically and thermally stable.
Discover bright