Assay Solution AN0106

AN0106: Human VEGF ELISA with Optimiser™ Microplates

Assay Solution for Invitrogen Human VEGF Antibody Pair (Catalog CHG0113)

Victor Moore; Applied Science Group, MiCo BioMed, Cincinnati, OH USA

Introduction:

MiCo BioMed’ Optimiser™-based ELISAs offer a rapid, sensitive, and specific chemifluorescent-based ELISA procedure for the measurement of analytes using very small sample volumes. The Optimiser™ plate is SBS/ANSI-compliant and is compatible with traditional 96-well microplate instrumentation.

A Human VEGF ELISA utilizing reagents from LIFE Technologies (Invitrogen, Catalog Number CHG0113) has been successfully transferred from a conventional 96-well ELISA plate format to an Optimiser™ microplate platform to achieve the following key performance benefits.

• Sample Volume: 5 μl • Assay time: Total assay time ≈ 2 hours (≈ 3.5 hour savings) • Assay reagents: ≈ 90% saving on antibody use 10 assays for the cost of 1 • Sensitivity/Range: > 4× improvement (23.4 – 1500 pg/ml) • Potential to increase sensitivity to ~ 1.2 pg/ml • Potential to achieve > 2-log dynamic range: 23.4 ~ 5700 pg/ml

Optimiser™ Method Development Process:

Please refer to the Assay Transfer Guide (Technical Support section of MiCo BioMed’s website) for details on the method development process. Each process step listed below requires 1 microplate (conventional for Step 1) and represents 1 experiment. In Step 2, the optimal coating buffer is selected from a panel of 12 coating buffers developed by MiCo BioMed.

Step 1:	Run a conventional ELISA to verify that the assay reagents perform as stated by the vendor(s). The human VEGF reagents were tested in a high-binding NUNC plate according to the protocol provided by the vendor. The operating range was confirmed to be 23.4 – 1500 pg/ml as recommended by vendor.
Step 2:	Select the optimal coating buffer for use with the Optimiser™-based ELISA. The coating buffer screening test showed that OptiBind™-F allows for most efficient binding of capture antibody to microfluidic channel surface.
Step 3:	Run antibody titrations to select the optimal capture and detection antibody concentrations. The titration study shows that 2.5 µg/ml of capture and 0.050 µg/ml of detection antibody exhibit best performance. As described further, this Optimiser™-based ELISA is more sensitive than a conventional plate ELISA and the user should determine the optimal antibody concentrations to maximize savings and achieve the desired operating range.

Note that while capture and detection antibody concentrations for Optimiser™-based ELISAs may be 2 -4 times greater than those used in conventional ELISAs; the total quantity of antibody used in Optimiser™-based methods is significantly lower than that used in conventional ELISAs due to the much smaller reagent volumes used in the Optimiser™-based methods. Furthermore, sensitivity can be readily “tuned” for Optimiser™-based ELISAs using the repeat loading approach and antibody use can be further minimized if desired.

Comparison of Antibody Requirements for Conventional and Optimiser™-based ELISAs.

Antibody Method Ab Concentration (μg/mL) Ab Vol./well (μL) Ab/Plate (μg) Savings Capture antibody Conventional* 1.25 1.00 12 90% ( Run 10 Optimiser™ plates for the capture antibody cost of 1 conventional ELISA plate)** Optimiser™ 2.5 5 1.2 Detection antibody Conventional* 0.025 100 0.24 90% ( Run 10 Optimiser™ plates for the detection antibody cost of 1 conventional ELISA plate)** Optimiser™ 0.050 5 0.024

*Vendor recommendation **Using material provided in listed catalog #’s

Optimiser™-Based ELISA and Results for Human VEGF:

The detailed procedure for this Optimiser™-based ELISA is contained in a companion document (User Manual or Detailed Experimental Protocol). The materials used in the procedure are specified in the Materials Table.

Brief assay protocol Add 5 μl of anti-human (Hu) VEGF capture antibody (2.5 μg/ml in OptiBind™-F); incubate for 10 min at RT. Add 5 μl of OptiWash™; wait 10 min. Add 5 μl of OptiBlock™; incubate for 10 min at RT. Add 5 μl standard, control, and samples; incubate 20 min at RT. (Prepare rHu VEGF in OptiBlock™ and samples in matrix-specific diluent) Add 5 μl of OptiWash™; wait 10 min. Add 5 μl of biotinylated anti-Hu VEGF detection antibody (0.050 μl/ml in OptiBlock™); incubate for 10 min at RT. Add 5 μl of OptiWash™; wait 10 min. Add 5 μl of SAv-HRP (provided in CHG0113; dilute to 0.05 μg/ml in OptiBlock™); incubate for 10 min at RT. Add 30 μl of OptiWash™; wait 10 min. Repeat step. Add 10 μl of OptiGlow™; wait 15 min; read.

The plate is read using an FLx800™ Fluorescence Microplate Reader (BioTek Instruments, Inc.) equipped with a 528/20 nm excitation filter and a 590/35 nm emission filter with a sensitivity setting of 44. The data is analyzed using Gen5™ software (BioTek Instruments, Inc.) and a standard curve is created by plotting human VEGF concentration vs background-adjusted RFU using a 4-parameter curve fit.

The standard curve range for the Optimiser™-based ELISA developed for human VEGF is 23.4 – 1500 pg/mL. The Optimiser™-based method is > 4-fold more sensitive than a conventional ELISA performed using the same reagents (Invitrogen TDS, Catalog Number CHG0113). The Optimiser™-based ELISA realized actual savings in time and labor (≈ 64 %), capture antibody (90%) and detection antibody (90%) (Reagent Savings Table) when compared with a conventional ELISA using the same materials at the vendor’s recommended concentrations. A further ≈ 95% savings in sample volume would be expected. Using the methods outlined in Application Notes (Technical Support section of MiCo BioMed’s website), the sensitivity of this assay can be projected at ≈ 1.2 pg/ml using the 20x sample repeat loading method and/or the operating range can be extended to > 2 logs using the modified substrate ratio.

 

Materials Used:

 

Material	Vendor	Vendor’s Catalog #	Vendor Contact
Human VEGF Antibody Pair	Invitrogen	CHG01131	www.invitrogen.com
NUNC Maxisorp microplate	Thermo Scientific	456537	1-800-625-4327
Optimiser™ microplate (with Holder) 2	MiCo BioMed	OPH-10	www.micobiomed-usa.com Product categories: • Optimiser™ microplates • OptiMax™ buffers
Polypropylene v-bottom plate		OPT/FL-231
Coat buffer test panel 3		OMR-TEST
Buffer reagent pack (with substrate) 2		OMR-10-J
Streptavidin-HRP for Optimiser™		OMR-HRP

1 Contains capture and detection antibodies, rHuman VEGF, and SAv-HRP.

2 Optimiser™ plates and corresponding OptiMax™ buffer reagents are also available in 2-plate and 50-plate configuration.

3 OMR-TEST is required only for assay transfer. FOR RESEARCH USE ONLY. Not for use in diagnostic procedures.