Patent Application: US-68126403-A

Abstract:
analytes are detected and / or quantified in electrolytic solutions suing surface enhanced raman scattering spectroscopy by adsorbing the analyte on the surface of an active metal electrode placed into an electrolytic solution being analyzed and which provide periodic regeneration or modulation of surface concentration of sers - active sites . as this occurs , the ambiguity of the measured values of the analyte signal , which is caused by instability of the surface activity of the sensor , is eliminated by optically normalizing to the total sers signal determined by active metal adatoms .

Description:
fig1 illustrates a sers spectrum of a hypothetical objected measured in the mode described above . for the sake of simplicity , the drawing illustrates only one of the vibration lines of the adsorbate spectrum . it is clear that in this case as well , the integral intensity of the adsorbate structural band is made up of a large combination of subsystems . however , in this case , the assemblage of these subsystems is uniform and is formed exclusively of adatoms with the adsorbed analyte particles . together with this , the shape of the analyte band in this case as well constitutes a non - uniform contour , made up of a multitude of such subsystems having various interactions among themselves . that is why , for a correct determination of an adsorbate concentration at normalization to adatomic component , one should bear in mind the entire combination of adatoms as reflected by the integral band of wide - band background . in other words the exact expression for determination of the adsorbate concentration looks as follows : wherein i a is the integral intensity of the sers spectrum vibration band ( the analyte band in fig1 a ) and i b is the intensity of the wide - band background . application of optical correlation spectroscopy methods , in combination with the above - mentioned technical solutions , makes possible significantly greater analytical sensitivity and selectivity of the sers method . these methods , among others , possess the greatest spectral analysis selectivity and sensitivity , and are especially effective in detecting structured spectral signals . the principle of optical correlation spectroscopy is based upon the use of optical recording devices , the hardware transmission function of which simulates the spectral function of the analyzed emission . in particular , in the widely used mask spectroscopy , this is ensured by using a mask having both transparent and non - transparent areas positioned on the pathway of the dispersed emission being analyzed ( novikov et al ., 1988 ). with the current state of the art electronic control devices , this effect can be achieved by special techniques of manipulating the optical selection device which provides scanning in preselected sequence of needed spectral sites by special programmed algorithms created on the basis of the measurement data on the sers spectra of individual components . if a spectrum of the analyzed emission has a quasiregular ( vibrational or vibrationally - rotational ) structure , and this is the type of emissions to which sers spectra pertain , the interference polarizing ( ip ) filters ( nekrasov et al ., 1998 ) known in spectroscopy are convenient for use in the sers hardware . the simplest of these devices , the so - called wood &# 39 ; s filter , consists of a retarder cut out parallel to the optical axis of a uniaxial crystal and placed between two polarizers . when the polarizers &# 39 ; axes are parallel or perpendicular to each other , and in such position make an angle of 45 ° to the crystal axis , the transmission spectrum of the ip filter constitutes a quasiperiodic set of transmission bands , determined by the interference results of polarized beams in the double - refracting crystal . when changing the relative direction of the polarizers &# 39 ; axes to 90 °, there takes place an inversion of peaks of the quasiperiodic picture , shown in fig2 a . as shown in fig2 a the spectral interval between the closest peaks ( half - width of the ip filter transmission band ) is defined by the thickness of the retarder and characteristics of the crystal material . when the direction of axes of a polarizer is aligned with the retarder axis ( and in such position is respectively at 45 ° to the axis of a second polarizer ), the quasiperiodic picture disappears and the system has a continuous transmission that reduces the transmitted light by half . considering the possibilities of the wood &# 39 ; s ip filter in an example of a detection diagram of a single line with a pedestal , imitating a typical situation for the sers , the results are shown in fig2 a and 2 b . fig2 a shows a portion of the ip filter transmission band for three different angles of the relative direction of the first and second polarizer axes ( 0 °, 45 °, 90 °). consideration of the other respective positions is insignificant , because they only lead to a lesser amplitude of the periodical structure with respect to the half continuous transmission . fig2 b depicts a structural line with a self - intensity i l , whose peak coincides with the axis of one of the ip filter transmission “ antinodes ” and which has a continuous pedestal ( background ) having intensity i b . as can be clearly seen from fig2 a and 2 b , with the relative direction of the polarizer axes at 90 °, when the ip filter transmission peak coincides with that of the structural line , the registered intensity is the sum of the line and background intensities : ( i 90 reg = i l + i b ). whereas with the mutually parallel axes position of both polarizers , the line intensity makes no contribution to the emission detected and only the background is registered : ( i 0 reg = i b ). hence , having measured the sers intensity at just these two relative polarizer axes positions , one can obtain all of the data necessary to determine an adsorbate concentration , including the normalizing parameter characterizing the adatomic component of the band . the expression to define an adsorbate concentration for this case is as follows : wherein the top indices of the intensity symbols mean the relative direction of the polarizer axes . together with this , the ip filter optical characteristics comprise another method for drastically increasing in the accuracy of measurement at the cost of minimizing the experimental errors related to the instability of an excitation source , registration system , oscillations of the average number of adsorbing centers in different regeneration cycles , etc . this possibility also lies in the constant component of the ip filter transmission and it ensures the ability to measure the complete integral intensity of the sers spectrum . this characteristic is perfect as an extra normalizing parameter for bringing the results of all of the serial measurements to a uniform fashion . a technical solution for an automatic device for quantitative analysis of the sers spectra , which would put into practice all of the above - mentioned possibilities of the ip filter - based optical correlation , is achieved by arranging the modulation of a filter transmission function through a periodical alteration of axis direction of rotation of one of the polarizers . this operation may be arranged in various ways by using trivial mechanical rotation of a polarizer , or by additional insertion of a controlled optically active modulator between a polarizer and a retarder . the algorithm for signal processing by such a periodical action device may be presented as follows : c = i ⁡ ( ω ) + i ⁡ ( ω + π 2 ) 2 ⁢ i ⁡ [ 2 × ( ω + π 4 ) ] × i ⁡ ( ω + π 2 ) wherein ω is the frequency of altering the polarization direction . the zero phase shift is corresponded by the relative direction of the polarizer axes position ensuring maximum ip filter transmission in a characteristic line or in a characteristic group of lines ( signature ) in the sers spectrum of an impurity ( adsorbate ) being analyzed . the foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can , by applying current knowledge , readily modify and / or adapt for various application such specific embodiments without undue experimentation and without departing from the generic concept . therefore , such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments . it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation . the means and materials for carrying out various disclosed functions may take a variety of alternative forms without departing from the invention . thus , the expressions “ means to . . . ” and “ means for . . . ” as may be found in the specification above and / or in the claims below , followed by a functional statement , are intended to define and cover whatever structural , physical , chemical , or electrical element or structures which may now or in the future exist for carrying out the recited function , whether or nor precisely equivalent to the embodiment or embodiments disclosed in the specification above . it is intended that such expressions be given their broadest interpretation . 1 . kneipp k ., kneipp h ., itzkan i ., dasari r . r ., feld m . s . chem . rev . 1999 . v . 99 . p . 2957 - 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