more preferably between 1 4 and 1 8 and most preferably about 1 6 in one embodiment of the seeding method the metal nanoparticles include surfactant along at least a portion of their length the surfactant present is generally associated with certain methods that can be used to form the nanoparticles the metal nanoparticles formed in the presence of surfactant are believed to display greater measurement sensitivity in another embodiment essentially spherical seeds nanospheres can be used and analysis upon measuring the absorption as described above for the u201c nucleating method u201d although nanospheres can be used with a diameter of 1 to 250 nm or even greater the extinction coefficient can not generally be treated as a constant for particles in excess of about 50 nm and corrections are generally included in the calculation of concentration of glucose nanosphere seeds having diameters of 5 to 50 nm can be used such as diameters of 5 to 10 nm or diameters of about 5 nm in the nucleation method a surfactant may also be added to the sensing solution certain surfactants referred to as coordinating surfactants can be used to control the shape of the nanoparticles formed such as to form shapes other than generally spherical particles which have been found to form in the absence of a surfactant body fluids in which glucose is found is known to include blood saliva urine and tears thus a variety of body fluids can be used with the invention however the glucose concentration in tears correlates well with the blood glucose concentration accordingly in an embodiment of the invention the body fluid is tears moreover tears include.