Patent Application
20110032521
The subject matter of this invention relates to surface enhanced Raman spectroscopy (SERS). More particularly, the subject matter of this invention relates to systems and methods for using high aspect ratio, metal particles for SERS.
Surface enhanced Raman spectroscopy (SERS) is a versatile technique for chemical analysis and biological detection. However, the use of SERS as a routine analytical technique has been hampered by the difficulty in obtaining consistent results and the wide variability in metal surfaces used to promote surface enhancements of the Raman signal. Active research is ongoing to remedy this drawback and enable spectroscopists to use SERS as a routine analytical technique.
Accordingly, the present invention solves these and other problems of the prior art by providing a new type of high aspect ratio metal particles with controlled size and surface roughness for use as surface enhanced Raman spectroscopy (SERS) substrates.
Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5. In certain cases, the numerical values as stated for the parameter can take on negative values. In this case, the example value of range stated as “less that 10” can assume negative values, e.g. −1, −2, −3, −10, −20, −30, etc.
According to various embodiments, there is a method of preparing a surface enhanced Raman spectroscopy (SERS) substrate 100 as shown in
In some embodiments, the step of providing a solution 110 of high aspect ratio metal particles in a solvent can include providing a solution 110 of high aspect ratio metal particles and one or more of a paint and a binder in a solvent.
The method of preparing a SERS substrate 100 can also include forming approximately one or more layers 130 of high aspect ratio metal particles on a substrate 120 by applying the solution 110 of high aspect ratio metal particles onto the substrate 120, as shown in
In another embodiment of the present teachings, the step of providing a solution 110 of high aspect ratio metal particles in a solvent 142 can include adding an immiscible solvent 144 to the solution of high aspect ratio metal particles and forming approximately a monolayer 135 of metal particles at the interface of two immiscible solvents 142 and 144. In various embodiments, the two immiscible solvents 142 and 144 can include polar solvent such as, for example, water and non polar solvent such as, for example, n-dodecane. The method of preparing a SERS substrate 100 can further include dipping a substrate 120 in the solution 110 of high aspect ratio metal particles, as shown in
In various embodiments, the method of preparing a SERS substrate 100 can also include depositing an analyte onto the substrate 120 (not shown). In other embodiments, the solution 110 of high aspect ratio metal particles can include analyte and thereby metal particles and analyte can be deposited onto the substrate simultaneously.
The method of preparing a SERS substrate 100 can further include removing any undesirable organic residue dissolved in the solvent. In various embodiments, the undesirable organic residue can be removed by oxidizing the organic residue using hydrogen peroxide or other oxidizing agent. In some embodiments, the SERS substrate 100 can be placed in about 40% to about 50% hydrogen peroxide solution and can be incubated at about 50° C. to about 70° C. for about 30 minutes to about 24 hours. In other embodiments, undesirable organic residue can be oxidized by heat treatments in air to a temperature of about 500° C. or other appropriate temperatures. In some other embodiments, undesirable organic residue can be removed by exposing the metal particles to a plasma, such as in a plasma cleaner. In other embodiments, fluorine from the surface of the high aspect ratio metal particles can be removed by placing the SERS substrate 100 in a solution of hydrochloric acid at a temperature from about room temperature to about 100° C. for about 30 minutes to about 24 hours and in some cases from about 50° C. to about 70° C. for about 1 hour to about 6 hours and drying the substrate 100 at about 50° C. In various embodiments, the disclosed SERS substrate 100 can be used with a variety of field deployable Raman spectrometers. Such a spectrometer is provided by several commercial sources such as Ocean Optics Inc. (Dunedin, Fla.) and Raman Systems Inc (Austin, Tex.).
According to various embodiments, there is another method of preparing a SERS substrate including mixing analyte and high aspect ratio metal particles with a transparent powder to form a mixture (not shown), wherein a major dimension of the high aspect ratio metal particles can be from approximately 10 to approximately 200 times a minor dimension of the high aspect ratio metal particles and pressing the mixture to form a pellet, wherein the transparent powder is transparent at the Raman laser wavelength and wherein the pellet can be used as SERS substrate for analyte analysis.
According to another embodiment of the present teachings, there is a method for enhanced detection of an analyte. The method can include adding an analyte to a solution of high aspect ratio metal particles, wherein a major dimension of the high aspect ratio metal particles can be from approximately 10 to approximately 200 times a minor dimension of the high aspect ratio metal particles and conducting at least one of Raman and fourier transform Raman analysis on the solution. In various embodiments, the enhancement can be up to about 105.
According to yet another embodiment of present teachings, there is a method for real time Raman analysis of cultured living cells. The method can include allowing endocytosis of high aspect ratio metal particles into an in-vitro cell culture, wherein a major dimension of the high aspect ratio metal particles can be from approximately 10 to approximately 200 times a minor dimension of the high aspect ratio metal particles. The method can further include conducting real time Raman analysis of the cell culture.
Examples are set forth herein below and are illustrative of different amounts and types of reactants and reaction conditions that can be utilized in practicing the disclosure. It will be apparent, however, that the disclosure can be practiced with other amounts and types of reactants and reaction conditions than those used in the examples, and the resulting devices various different properties and uses in accordance with the disclosure above and as pointed out hereinafter.
Several SERS substrates were prepared using a variety of support materials, including magnesium fluoride, stainless steel, glass, quartz, and silicon. Deposition was performed by trapping the hydrophobic gold particles at a polar nonpolar interface and either dip coating the particles onto the support substrate or by placing a droplet containing the particles on the support substrate. The polar phase was water purified to a specific resistivity of 18 MΩ and the non-polar phase consisted of n-dodecane (Acros Organics USA, Morris Plains, N.J.) although other aliphatic hydrocarbons could be used. The gold particles formed a pseudo-monolayer over the support substrate. After deposition, the substrates were placed in an oven at about 60° C. until dry. After drying, the substrates were subjected to cleaning, first with about 1M HCl (Fisher Scientific USA, Pittsburgh, Pa.) and then with about 25% to about 50% hydrogen peroxide (Fisher Scientific USA, Pittsburgh, Pa.) for up to about 48 hours at about 60° C. to remove organic contaminants. Alternatively, the substrates can be cleaned with a plasma cleaner (Harrick Plasma, 2-4 minutes, Ar process gas).
The SERS substrates prepared in Example 1 were evaluated with urea (Fisher Scientific USA, Pittsburgh, Pa.) as analyte as a test case at a concentration of about 50 mM and about 0.5 mM. One microliter droplet was placed on each of the substrates and allowed to dry. The substrates were analyzed with an in Via™ Raman microscope system (Renishaw, UK) having a laser excitation source at about 785 nm. Samples were scanned from about 200 cm−1 to about 2000 cm−1 at varying laser power and magnification. Glass showed a wide Raman peak at 1360 cm−1 that could masked the analyte peaks, making it less desirable as a support material for urea. Both magnesium fluoride and silicon showed one characteristic peak at about 480 cm−1 and about 520 cm−1 respectively. However, these characteristic peaks of magnesium fluoride and silicon were usually masked by the gold particles and were not readily observed on the substrates and therefore they functioned well as SERS substrate material. Stainless steel and quartz did not contribute any characteristic peaks in the range scanned and performed also well as SERS substrates for urea. Surface enhancement of up to about 105 was observed in these SERS substrates.
While the invention has been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” As used herein, the phrase “X comprises one or more of A, B, and C” means that X can include any of the following: either A, B, or C alone; or combinations of two, such as A and B, B and C, and A and C; or combinations of three A, B and C.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
This application claims priority to U.S. Provisional Patent Application Ser. No. 60/972,438 filed on Sep. 14, 2007, and is a national phase application of PCT/US2008/076166 filed on Sep. 12, 2008, the disclosure of which is incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/76166 | 9/12/2008 | WO | 00 | 8/9/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60972438 | Sep 2007 | US |
