Abstract:
The present invention relates to an aflatoxin-detection device. The aflatoxin-detection device includes a flow path for a test solution and a plurality of nanocompo site strips disposed within the flow path. Each nanocomposite strip of the plurality of nanocomposite strips is arranged in a spaced parallel relationship with a successive nanocomposite strip of the plurality of nanocomposite strips. The plurality of nanocomposite strips exhibit high affinity for aflatoxin. Absorption of aflatoxin induces fluorescence of the plurality of nanocomposite strips. Responsive to a fluorescence intensity of each nanocomposite strip of the plurality of nanocomposite strips, a concentration of aflatoxin in the test solution is determined.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to, and incorporates by reference the entire disclosure of, U.S. Provisional Patent Application No. 61/826,844, filed May 23, 2013. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to sensors for detection of toxins and more particularly, but not by way of limitation, to sensors utilizing a smectite-polymer nanocomposite coating for detection of aflatoxins. 
         [0004]    2. History of the Related Art 
         [0005]    Aflatoxins, a harmful byproduct of mold, represent a major type of biological toxin responsible for both acutely toxic and carcinogenic effects on humans and animals alike. Contamination of agricultural commodities, human foods, and animal feeds with aflatoxins have resulted in significant concerns for the food industry. Rapid, quantitative, and low-cost detection methods are important for the timely evaluation, monitoring, and mitigation of hazardous effects caused by aflatoxins. 
       SUMMARY 
       [0006]    The present invention relates generally to sensors for detection of toxins and more particularly, but not by way of limitation, to sensors utilizing a smectite-polymer nanocomposite coating for detection of aflatoxins. In one embodiment, the present invention relates to an aflatoxin-detection device. The aflatoxin-detection device includes a flow path for a test solution and a plurality of nanocomposite strips disposed within the flow path. Each nanocomposite strip of the plurality of nanocomposite strips is arranged in a spaced parallel relationship with a successive nanocomposite strip of the plurality of nanocomposite strips. The plurality of nanocomposite strips exhibit high affinity for aflatoxin. Absorption of aflatoxin induces fluorescence of the plurality of nanocomposite strips. Responsive to a fluorescence intensity of each nanocomposite strip of the plurality of nanocomposite strips, a concentration of aflatoxin in the test solution is determined. 
         [0007]    In another embodiment, the present invention relates to a method for detecting aflatoxin. The method includes conducting a test solution through a flow path formed in an aflatoxin-detection device. The flow path includes a plurality of nanocomposite strips formed therein. The method also includes exposing the aflatoxin-detection device to ultraviolet illumination. The ultraviolet illumination induces fluorescence of certain nanocomposite strips of the plurality of nanocomposite strips. Responsive to a fluorescence intensity of the certain nanocomposite strips, a concentration of aflatoxin in the test solution is determined. 
         [0008]    In another embodiment, the present invention relates to a method for producing an aflatoxin-detection device. The method includes forming a stencil having a plurality of parallel slots, applying the stencil to a substrate, and applying a plurality of nanocomposite strips to the substrate utilizing the stencil. The method also includes removing the stencil from the substrate, forming a flow layer, and coupling the flow layer to the substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which: 
           [0010]      FIG. 1  is an exploded perspective view of an aflatoxin-detection device according to an exemplary embodiment; 
           [0011]      FIG. 2  is a flow diagram of a process for making an aflatoxin-detection device according to an exemplary embodiment; 
           [0012]      FIG. 3A  is a schematic diagram of an aflatoxin-analysis system according to an exemplary embodiment; 
           [0013]      FIG. 3B  is a flow diagram of a process for using an aflatoxin-detection device according to an exemplary embodiment; 
           [0014]      FIG. 4  is a graph of fluorescence intensity according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Various embodiments of the present invention will now be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
         [0016]    Aflatoxin detection is currently performed using high-performance liquid chromatography (“HPLC”) followed by fluorometric or mass spectroscopic analysis. This is a very time consuming and costly procedure and, as a result, has been primarily limited to laboratory use. A number of rapid-detection methods based on immunoassays have also been developed. These rapid-detection methods utilize antibodies to selectively capture aflatoxins in a test solution. These rapid-detection methods have limitations. First, they are susceptible to denaturation and degradation and, as a result, require very strict testing conditions for their effective functioning. Second, the production of antibodies requires live animal and can be a complex and expensive process. 
         [0017]    Several bentonites (smectite-rich clays) have been used as adsorbent additives to detoxify aflatoxin-contaminated animal feeds. Recent studies have demonstrated that divalent cations and transition cations in the interlayers of smectite can induce the substantial bonding of the aflatoxin to the smectite. Unlike antibodies, the smectite-aflatoxin binding is hardly affected by various adsorption conditions such as, for example, temperature or pH value. In addition, a high adsorption capacity such as, for example, 11&gt;-20% of the self weight of the smectite can also be obtained due to the large surface area (about 800 m2/g) of the smectite interlayers. Because of its high absorption selectivity and capacity for aflatoxin, smectite could be developed into a new molecular recognition agent for the aflatoxin detection, serving as an inexpensive inorganic substitute for the delicate and costly antibodies. 
         [0018]      FIG. 1  is an exploded perspective view of an aflatoxin-detection device  100 . The aflatoxin-detection device  100  includes a substrate layer  102  that is coupled to a flow layer  106 . In a typical embodiment, the substrate layer  102  is, for example, a glass microscope slide, however, other appropriate materials may be utilized. A plurality of nanocomposite strips  104  are disposed on a surface of the substrate layer  102  at regular-spaced intervals. In a typical embodiment, the nanocomposite strips  104  are constructed of a clay mineral such as, for example, Smectite-polyacrylamide. The flow layer  106  includes a flow path  108  formed in a surface facing the substrate layer  102 . In a typical embodiment, the flow path  108  in formed through a process such as, for example, photo-lithography, and has a depth of approximately 10 μm. The flow path  108  includes a plurality of parallel sections  109 . The plurality of parallel sections  109  are fluidly coupled by bends  113 . An inlet port  110  and an outlet port  112  are fluidly coupled to respective ends of the flow path  108 . Tubing  115  such as, for example, polyamide tubing is fluidly coupled to the inlet port  110  and the outlet port  112 . When the flow layer  106  is assembled to the substrate layer  102 , the nanocomposite strips  104  are enclosed within the flow path  108 . 
         [0019]    Still referring to  FIG. 1 , in a typical embodiment, the nanocomposite strips  104  are synthesized on flat silicon substrates via a layer-by-layer assembling process utilizing 1 g/L polyacrylamide aqueous solution and 1 g/L Smectite dispersion. A group of pre-cleaned silicon substrates are immersed into the polyacrylamide aqueous solution for, for example, seven minutes and then rinsed in deionized water. Next the silicon substrates are immersed in the Smectite dispersion for, for example, five minutes and then rinsed in deionized water. This cycle is repeated until the silicon substrate is fully covered with a nanocomposite film. By way of example, the optimal polyacrylamide concentration has been shown to be approximately 0.005%. 
         [0020]      FIG. 2  is a flow diagram of a process  200  for making the aflatoxin-detection device  100 . The process  200  starts at step  202 . At step  204 , a stencil is formed from a transparency sheet. The stencil includes a plurality of regular-spaced generally-parallel slots. The stencil is applied to the substrate layer  102  and secured thereto via, for example, a binder clip. At step  206 , the nanocomposite strips  104  are applied to the substrate layer  102  utilizing the stencil. The nanocomposite strips  104  are applied in the regular-spaced generally parallel slots of the stencil. At step  208 , the stencil is removed from the substrate layer  102  leaving the nanocomposite strips  104  properly located on the substrate layer  102 . At step  210  the flow layer  106  is formed. A flow-path pattern is formed on, for example, a silicon wafer. The flow path  108  is formed then formed in the flow layer  106  via, for example, photolithography. At step  212 , the flow layer  106  is coupled to the substrate layer  106  such that the nanocomposite strips  104  are enclosed in the parallel sections  109  of the flow path  108 . At step  214 , the tubing  214 , such as, for example, polyamide tubing, is fluidly coupled to the inlet port  110  and the outlet port  112 . The process  200  ends at step  216 . 
         [0021]      FIG. 3A  is a schematic diagram of an aflatoxin-analysis system  300 . The aflatoxin-analysis system  300  includes an ultraviolet lamp  302 . The aflatoxin-detection device  100  is positioned under the ultraviolet lamp  302  such that ultraviolet light  304  emitted from the ultraviolet lamp  302  is incident upon the aflatoxin-detection device  100  at an angle (θ). 
         [0022]    Still referring to  FIG. 3A , fluorescence intensity from aflatoxin adsorbed to the nanocomposite strips  104  is proportional to the concentration of aflatoxins in the test solution. Thus, under normal ultraviolet illumination (θ=0 degrees), uniform fluorescence emission will be observed from the nanocomposite strips  104 . As shown in  FIG. 3A , under oblique illumination (θ&gt;0 degrees), as a distance between a nanocomposite strip  104  increases, a fluorescence intensity emitted from the nanocomposite strip  104  decreases. In this scenario, the average excitation intensity on a nanocomposite strip (x) is expressed in formula 1 below: 
         [0000]    
       
         
           
             
               
                 
                   
                     I 
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                       ( 
                       x 
                       ) 
                     
                   
                   = 
                   
                     
                       I 
                       0 
                     
                     
                       
                         h 
                         2 
                       
                       + 
                       
                         x 
                         2 
                       
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0000]    Where I(x) is the is the excitation intensity of the nanocomposite strip (x), I 0  is the intensity of the ultraviolet lamp  302 , h is the vertical distance between the aflatoxin-detection device  100  and the ultraviolet lamp  302 , and x is the horizontal distance between the ultraviolet lamp  302  and the nanocomposite strip (x). 
         [0023]    The fluorescence intensity of the nanocomposite strip (x) is expressed in formula 2 below: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       I 
                       fi 
                     
                      
                     
                       ( 
                       x 
                       ) 
                     
                   
                   ∝ 
                   
                     
                       C 
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                         I 
                         0 
                       
                       
                         
                           h 
                           2 
                         
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                           x 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
         [0024]    Where I fi  is a fluorescence intensity of the nanocomposite strip (x) and C i  is a concentration of aflatoxin in the test solution. This correlation makes it possible to achieve a quantitative determination of aflatoxin concentration in the test solution by counting a number of fluorescing nanocomposite strips. 
         [0025]      FIG. 3B  is a flow diagram of a process  350  for using the aflatoxin-detection device  100 . The process starts at step  352 . At step  354 , the aflatoxin-detection device is fluidly coupled to a test-solution source. In a typical embodiment, the testing solution is conducted to the aflatoxin-detection device via the tubing  115  such as, for example, polyamide tubing. The tubing is fluidly coupled to the inlet port  110  and the outlet port  112  of the aflatoxin-detection device. At step  356 , the testing solution is conducted through the flow path  108  of the aflatoxin-detection device  100 . The testing solution may be conducted through the flow path  108  for a period of time of approximately 2 minutes up to approximately 20 minutes or more. 
         [0026]    The nanocomposite strips  104  absorb molecules of aflatoxin that are present in the test solution. Absorption of aflatoxin molecules results in a highly concentrated accumulation of aflatoxin molecules in the nanocomposite strips  104 . At step  360 , the aflatoxin-detection device  100  is observed under ultraviolet illumination and a fluorescent intensity of the nanocomposite strips  104  is observed. At step  362 , a concentration of aflatoxin present in the test solution is determined based upon the fluorescent intensity of the nanocomposite strips  104 . The process  350  ends at step  364 . 
         [0027]    In a typical embodiment, when the aflatoxin-detection device  100  is illuminated under oblique ultraviolet illumination, a fluorescence intensity of the nanocomposite strips 104 decreases as a distance from the ultraviolet lamp  302  increases. Oblique ultraviolet illumination creates a non-uniform illumination field with a large gradient along a length of the aflatoxin-detection device  100 . The aflatoxin-detection device  100  exhibits high sensitivity and linearity. The nanocomposite strips  104  exhibit a high affinity for aflatoxin molecules thus giving the aflatoxin-detection device  100  a high degree of sensitivity. Further, because the fluorescence intensity of aflatoxin is proportional to the concentration of aflatoxin, the aflatoxin-detection  device  100  also provides a high-degree of linearity for aflatoxin detection. 
         [0028]      FIG. 4  is a graph of fluorescence intensity of the nanocomposite strips  104  according to an exemplary embodiment. A threshold fluorescence intensity Ith represents a weakest fluorescence that can be visually distinguished. An intercept point between I f i (x) curves and the Ith line determines a number of nanocomposite strips  104  (Nj), which can be effectively observed visually. Higher aflatoxin concentration in the test solution leads to more adsorption on the nanocomposite strips  104  and a larger number of observable nanocomposite strips  104 . This correlation makes it possible to achieve a quantitative estimation of aflatoxin concentration in the test solution by just counting the number of “fluorescing” nanocomposite strips  104  without involving sophisticated spectrofluorometers. 
         [0029]    High absorption capacity of the nanocomposite strips  104  allows the aflatoxin-detection device  100  to detect very low levels of aflatoxin such as, for example, in the range of approximately 10 parts per billion. Furthermore, the nanocomposite strips  104  are unaffected by the presence of other organic or inorganic compounds. The nanocomposite strips  104  also exhibit structural and chemical stability, thereby allowing the aflatoxin-detection device  100  to have a long shelf life. Finally, the aflatoxin detection device  100  allows detection of aflatoxin in a period of time of, for example, approximately 10 minutes or less. 
         [0030]    Although various embodiments of the method and system of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Specification, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit and scope of the invention as set forth herein. It is intended that the Specification and examples be considered as illustrative only.