DMSO by itself is reported to have antioxidant action and thus there exists  problem in using it as a solvent for antioxidant activity. 

Check this link

http://www.sciencedirect.com/science/article/pii/S1056871910001620

Dimethyl sulfoxide is an amphiphilic compound whose miscibility with water and its ability to dissolve lipophilic compounds make it an appreciated solvent in biomedical research. However, its reported antioxidant properties raise doubts about its use as a solvent in evaluating new antioxidants. 

Dimethyl sulfoxide is a very useful solvent that may be used at relatively low concentrations for study of antioxidant activity

DMSO has redox properties. It can be reduced to DMS and oxidized to the sulfone.

Dear Varsha Dilip-Jadhav

what is the save concentration that can be sed

Which plant extract? is an important issue, may use DMSO as a solvent. Along with antioxidant properties see other important properties also.

There are some issues related to safety of DMSO, that you have to keep in mind.

I think that dimethyl sulfoxide is a very useful solvent that may be used at relatively low concentrations for study of antioxidant activity. However, its reported antioxidant properties raise doubts about its use as a solvent in evaluating new antioxidants. 

I think u can use DMSO keeping an eye on the conc and using sham/vehicle control in ur experiments.

I think you should use methanol or water instead DMSO as solvent. What is the reason? Did your sample not soluble in organic solvent?

I agree with Mohan Mukherjee

DMSO can effectively be used as stock solution of plant extracts for antioxidant screening.

You can use DMSO as stock solution. Dimethyl sulfoxide (DMSO), a by-product of the wood industry, has been in use as a commercial solvent since 1953. It is also one of the most studied but least understood pharmaceutical agents of our time--at least in the United States. According to Stanley Jacob, MD, a former head of the organ transplant program at Oregon Health Sciences University in Portland, more than 40,000 articles on its chemistry have appeared in scientific journals, which, in conjunction with thousands of laboratory studies, provide strong evidence of a wide variety of properties. (See Major Properties Attributed to DMSO) Worldwide, some 11,000 articles have been written on its medical and clinical implications, and in 125 countries throughout the world, including Canada, Great Britain, Germany, and Japan, doctors prescribe it for a variety of ailments, including pain, inflammation, scleroderma, interstitial cystitis, and arthritis elevated intercranial pressure.

DMSO is a polar aprotic solvent and is less toxic than other members of this class, such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and HMPA. DMSO is frequently used as a solvent for chemical reactions involving salts, most notably Finkelstein reactions and other nucleophilic substitutions. It is also extensively used as an extractant in biochemistry and cell biology.[11] Because DMSO is only weakly acidic, it tolerates relatively strong bases and as such has been extensively used in the study of carbanions. A set of non-aqueous pKa values (C-H, O-H, S-H and N-H acidities) for thousands of organic compounds have been determined in DMSO solution.[12][13]

Because of its high boiling point, 189 °C (372 °F), DMSO evaporates slowly at normal atmospheric pressure. Samples dissolved in DMSO cannot be as easily recovered compared to other solvents, as it is very difficult to remove all traces of DMSO by conventional rotary evaporation, one technique to fully recover samples is removal of the organic solvent by evaporation followed by addition of water (to dissolve DMSO) and lyophilisation to remove both DMSO and water. Reactions conducted in DMSO are often diluted with water to precipitate or phase-separate products. The relatively high freezing point of DMSO, 18.5 °C (65.3 °F), means that at, or just below, room temperature it is a solid, which can limit its utility in some chemical processes (e.g. crystallization with cooling).

In its deuterated form (DMSO-d6), it is a useful solvent for NMR spectroscopy, again due to its ability to dissolve a wide range of analytes, the simplicity of its own simple spectrum, and its suitability for high-temperature NMR spectroscopic studies. Disadvantages to the use of DMSO-d6 are its high viscosity, which broadens signals, and its hygroscopicity, which leads to an overwhelming H2O resonance in the 1H NMR spectrum. It is often mixed with CDCl3 or CD2Cl2 for lower viscosity and melting points.

DMSO is finding increased use in manufacturing processes to produce microelectronic devices. It is widely used to strip photoresist in TFT-LCD 'flat panel' displays and advanced packaging applications (such as wafer-level packaging / solder bump patterning). It also used in biopreservation especially stem cell banking. DMSO is an effective paint stripper, being safer than many of the others such as nitromethane and dichloromethane.

Because of its ability to dissolve many kinds of compounds, DMSO plays a role in sample management and high-throughput screening operations in drug design.