Abstract:
A surface enhanced Raman scatter (SERS) analyte analyzer. The analyzer has floating surfaces for enhancement of the Raman scattered light from sample molecules. An injector may provide a spray of charged nanoparticles suspended in droplets of an evaporable solution into a chamber. When the solution quickly evaporates, droplets of nanoparticles are left without a supporting solution. These droplets or cloud of charged nanoparticles may then explode into a dispersion or aerosol. The charged nanoparticles may attract molecules of a sample for attachment to their surfaces. A laser light may impinge the attached molecules which may result in surface enhanced Raman scattered light received by a detector or a light spectrometer. Wavelength signatures may then be obtained from the spectrometer. The signatures may provide information about the molecules.

Description:
BACKGROUND 
       [0001]    The invention relates to analyzers and particularly to light scattering analyzers. More particularly, the invention pertains to Raman light scattering analyzers. 
       SUMMARY 
       [0002]    The invention is an analyzer based on electro-spray ionization and surface enhanced Raman scattering. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0003]      FIG. 1  is a diagram of a basic layout of the present analyzer; 
           [0004]      FIG. 2  is a diagram showing a chamber having inputs for a sample and nanoparticle solution, and an evolving nanoparticle droplet; and 
           [0005]      FIG. 3  reveals the chamber with an interaction of the analyte with nanoparticles. 
       
    
    
     DESCRIPTION 
       [0006]    The breath of a person may contain rich information about that person, which may include the person&#39;s well being, nutrition, dietary habits, and so forth. A monitoring of the content of breath may offer great potential in clinical diagnosis, monitory ring, forensic science, and other fields. However, current technology such as mass spectroscopy, FTIR, colorimetry, and other technologies have limitations such as labeling required, non-real time measurements, difficulties of miniaturization, and more. 
         [0007]    One may propose to integrate an electrical spray ionization device (ESI) based real-time nanoparticle sprayer with a surface enhanced Raman scattering (SERS) light source and detector for breath analysis. A nanoparticle solution may be made up of multiple types of functionalized nanoparticles with suitable solvent. During a spray, nanoclusters may be formed and analytes from a breath may bond or attach to the nanoparticles of the nanoclusters. A SERS signal may then be detected. This technique may feature miniaturizable, label-free, real-time, high sensitivity, and multiplexing. An example application of the present approach may include a portable ESI-SERS based breath analyzer. This analyzer may be used in clinics, resource-limited areas for disease monitoring, exposure identification, and so on. 
         [0008]      FIG. 1  is a diagram of an illustrative implementation of the present invention. This implementation may be a breath analyzer  10 . Analyzer  10  may have a support structure  11  which may contain a port  12  for an injection of a nanoparticle spray  19  from an ESI nozzle  15  through the port into a chamber  14 . Another port  13  may be an inlet for conveying a sample of analyte  16 , such as a breath or some other matter for analysis into the chamber  14 . The analyte  16  and the spray  19  may combine into a combination  23  of analyte  16  with molecules attached to the nanoparticles  28  from the spray  19 . Port  13  may have an applicable mechanism  24  for conditioning the matter containing analyte  16 , such as a breath. Mechanism  24  may be, for example, a filter for removing particles and moisture from the sample. There may be a light source and detector  17  situated at one end of chamber  14  for emanating a light  21  and detecting light  22  scattered by the combination  23 . The emanated light  21  and detected light  22  may be provided to and conveyed from the chamber  14 , respectively, with an optical fiber or other mechanism  38 . At the other end of chamber  14  may an outlet  18  for an exhaust of the product  23  of matter  16  and nanoparticles  28 . A voltage may be applied across a metal pad  25  and nozzle  15 , with the positive polarity connected to the nozzle. The polarity could instead be applied in reverse. 
         [0009]      FIG. 2  reveals further details of the present system  10 . A D.C. voltage source  26  of about 1000 volts may have a positive terminal connected to the nozzle  15  and a negative terminal connected to the cathode pad  25 . Source  26  may be a battery or some other provision. A colloid of silver (Ag) nanoparticles  28  suspended in a solution  27  may be provided to nozzle  15  in the port  12 . Other metals, in addition to silver, such as gold, copper, and/or other noble metals, may be used as nanoparticles. This colloid of nanoparticles may be pushed through the nozzle  15  which may have a needle-like exit tip  29 . The solution  27  may have nanoparticles  28  with positive charges (i.e., like ions) due to the positive voltage applied to the metal nozzle  15  relative to the cathode pad or plate  25  which may be connected to an electric charge generator or source. The solution or fluid may flow out of the tip in a form of a capillary jet  32  with a cone-shaped base  31  at the tip of the nozzle that narrows down to a fine liquid filament or jet  32 . The base  31  form of the exiting solution may be regarded as a Taylor cone. There may be a spraying of SERS-active nanoparticles  28  suspended in the solution  27 . Interfacial instabilities may break this filament  32  into droplets  33  of charged Ag nanoparticles  28  to form a plume  37 . The solution may rapidly evaporate resulting in droplets without solution or cloud  34  of nanoparticles  28  in the plume  37 . Each droplet  34  may subsequently result in a (Coulombic) break up or explode into individually bare and charged Ag nanoparticles  28  as shown in a dispersion  35  of particles  28  in  FIG. 3 . The nanoparticles of this nature may be regarded as being aerosolized or an aerosol  35 . 
         [0010]    An illustrative purpose of these nanoparticles  28  of chamber  14  is shown in  FIG. 3 . Molecules  36  from the sample  16 , such as a breath, may attach to the charged Ag nanoparticles  28  floating in a vacuum, air or the like, in chamber  14 . The nanoparticles  28  may be effectively an aerosol that constitutes a floating substrate for surface enhanced Raman scattering (SERS). There may be a flow of nanoparticles  28 , many with molecules  36  attached, (e.g., nanoparticle attached molecule ensembles  39 ), towards the exhaust port  18  of  FIG. 1 . 
         [0011]    Light  21 , such as laser light, may be directed at one or more molecules  36  attached to the surfaces of nanoparticles  28 . Enhanced surface Raman scattered light  22  may exit from the molecules  36  chamber  14  to a light spectrometer, e.g., a Raman spectrophotometer. SERS signatures may be read from the spectrometer, which may provide information about and/or identify the respective molecules  36 . 
         [0012]    To lead into a background of the present system, it may be noted that when light is scattered from an atom or molecule, most photons are elastically scattered (i.e., Rayleigh scattering). The scattered photons may have the same frequency as the incident photons. However, a small fraction of light (e.g., about 1 in 10 7  photons) may be scattered at frequencies different from the frequency of the incident photons. This may be a result of inelastic scattering. Such scattered light may provide information about the molecules vibrational quantum states. Although Raman scattering may occur with a charge in vibrational, rotational or electronic energy of a molecule; a primary concern is the vibrational Raman effect. 
         [0013]    There may be several kinds of Raman scattering. If a molecule absorbs energy (i.e., the resulting photon has lower energy), then one has Stokes scattering. If the molecule loses energy (i.e., the resulting photon has higher energy), then one has anti-Stokes scattering. The Stokes spectrum may be more intense than the anti-Stokes spectrum since a Boltzmann distribution may indicate that more molecules occupy lower energy levels than the higher levels in most cases. An absolute value should not depend on Stokes or anti-Stokes scattering. The energies of the different vibrational levels are of significance. The intensities of the Raman bonds may be dependent just on a number of molecules occupying different vibrational states, when the scattering process occurs. 
         [0014]    The rather weak Raman effect or scattering (i.e., relative to the Rayleigh scattering) from molecules may be greatly strengthened (by a factor of up to 14 orders of magnitude) if the molecules are attached to a surface such as that of metallic nanostructures, e.g., colloidal silver particles. This phenomenon of increased intensity of Raman scattering may be referred to as surface-enhanced Raman scattering (SERS) which appears strongest on silver, but is observable on gold and copper. 
         [0015]    Surface-enhanced Raman scattering may arise from several mechanisms. One may be an enhanced electromagnetic field produced at the surface of the metal. When the wavelength of the incident light is close to the plasma wavelength of the metal, conduction electrons in the metal surface may be excited into an extended surface electronic excited state called a surface plasmon resonance. Molecules adsorbed or in close proximity to the surface may experience an exceptionally large electromagnetic field. Vibrational modes normal to the surface tend to be most strongly enhanced. 
         [0016]    Another mode of enhancement may be by a formation of a charge-transfer complex between the surface and the analyte molecule. Electronic transitions of many charge transfer complexes may be in the visible range, where a resonance enhancement can occur. 
         [0017]    Molecules with a lone pair electrons or pi clouds may show the strongest SERS. The effect was apparently noted with pyridine. Aromatic nitrogen or oxygen containing compounds, such as aromatic amines or phenols, may be strongly SERS active. The effect may also be seen with other electron-rich functionalities such as carboxylic acids. 
         [0018]    The intensity of a surface plasmon resonance may be dependent on many factors including the wavelength of incident light and the morphology of the metal surface. The wavelength should match the plasma wavelength of the metal. This wavelength may be about 382 nm for a 5 μm silver particle, but could be as high as 600 nm for larger ellipsoidal silver particles. 
         [0019]    An advantage of the present invention may include a high capturing efficiency of high mono or poly molecules. Proteins, small molecules, pollen, anything that can flow through the chamber  14  in a gas phase, may be detected. An example application may include a sniffer. No sample preparation is necessarily needed. The particle capture may be 93 to 98 percent. The present system may be fluorescent signal insensitive. The high energy increase of the surface enhanced approach may be even greater with charged nanoparticles compared to the classical surface substrate approach of enhancement. That is because the molecules are drawn closer to a charged floating substrate, i.e., charged nanoparticles suspended in space. Detection of certain molecules may occur at as low as 30 ppt. The present system may operate at room temperature. It may used as a portable mass spectrometer. It can function with a flow rate of spray as low as one nL/min. Yet the air flow rate in the chamber may be as fast as meters per second. Consequently, an analysis may be fast (i.e., within milliseconds). For these and other reasons, the present system has advantages relative to the ordinary surface-enhanced Raman scattering approach. 
         [0020]    In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense. 
         [0021]    Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.