Alejandro J. Gimenez

The encapsulation of magnetic nickel nanowires (NiNWs) with gelatin is proposed as an alternative for optical label detection. Magnetic nanowires can be detected at very low concentrations using light-scattering methods. This detection capacity could be helpful in applications such as transducers for molecular and biomolecular sensors; however, potential applications require the attachment of specific binding molecules to the nanowire structure. In the present study, a method is presented which is helpful in coating magnetic nanowires with gelatin, a material with the potential to handle specific decoration and functionalization of the nanowires; in the first case, silver nanoparticles (AgNPs) are efficiently used to decorate the nanowires. Furthermore, it is shown that the synthesized gelatin-coated particles have excellent detectability to the level of 140 pg/mL; this level of detection outperforms more complex techniques such as ICP-OES (~3 ng/mL for Ni) and magnetoresistance sensing (~10 ng/mL for magnetic nanoparticles).

Herein we describe a method to measure turbidity in liquids by probing a graphic pattern by optical transmission. Data are collected by a video camera and a mathematical algorithm is used to correlate image loss with turbidity. We report high-resolution turbidity measurements of nanoparticle colloids to assess the proposed methodology. Measurements are differentially performed which helps reduce noise from external sources. Using Nephelometric Turbidity Units (NTU) standards we obtain detectable measurements in a broad range of NTU from 1.95 to 1000. By implementing the proposed methodology, we proposed a video-based inexpensive yet reliable turbidimetry instrument.

In this paper, we report the development of an oxygen sensor using a simple device made from a film of ZnO crystals dispersed over a paper surface. Due to the high porosity of this kind of device made from paper and ZnO, a large photoconductive effect is observed as result of the fast absorption and desorption of oxygen from the ZnO surface. To detect oxygen, we propose to use ultraviolet (UV) illumination over the photoconductive surface of the sensor, the applied UV light produces oxygen desorption causing current variations through the sensor that are proportional to the oxygen presence nearby the sensor surface. The sensor developed in this paper is attractive because it is remarkably easy to fabricate, employs only very low-cost materials for its construction, and shows a better sensitivity at low concentration of oxygen at partial vacuum environments.

We report the preparation of Ni nanowire colloidal suspension that exhibits large light scattering changes when a magnetic field is applied. These changes occur during the application of alternating transversal magnetic fields. The intensity variation can easily be detected and measured since the light signal produced is very large with ratios much larger compared with signals obtained from light transmission through the nanowire colloidal suspension. Ni nanowires used for the experiments are about 1.2 μm long and 50 nm in diameter; suspensions of 44 μg/ml of these nanowires yield a scattering light variation ratio up to 35% when subjected to transversal alternating magnetic fields of 10 G. The methodology proposed could be implemented to detect and characterize magnetic nanowires even at concentrations as low as 4.4 μg/ml. Using finite element modeling, we observe that nanowires in a suspension scatter light depending strongly on the incidence angle of the applied light. From the finite element simulations, we also observe that nanowires may present plasmonic-antenna absorption effects that can be useful to indirectly measure nanowire properties, such as length and composition.

An electronic control system has been developed for a Raman spectrometer by using electronics based on microcontroller technology. With these microcontrollers it is possible to emulate control circuitry capable of performing complex tasks, such as the monochromator step motor control and the photomultiplier pulse count required in the Raman spectroscopy process. This approach could be used to give new life to valuable scientific instruments and tools. The Raman spectrometer control built is now fully functional and compatible with Windows 7. Raman spectra from well-known materials are presented to compare results and in order to confirm the proper operation of the developed control system

With very simple methods, we fabricate photoelectrical devices using a regular paper as substrate; these sensors are able to detect ultraviolet, visible, and infrared radiation using different paper additives. The experiment we made to test detection of ultraviolet and visible light consists in irradiating light of different wavelengths over a device made of paper and semiconductor crystals; electrical current of these devices increases importantly when the bandgap energy of the semiconductor crystal is reached. To test the sensitivity to infrared, we use paper devices impregnated with salts and glycerol to increment its electrical conductivity due to the augmentation of ionic current carriers. We observe that the ionic conductivity on paper increases when the paper is irradiated by infrared light from hot objects; this phenomenon might be due to the molecular structure of cellulose that absorbs energy in the infrared part of the spectrum.

We develop a mathematical procedure to simulate and analyze circuits of molecular devices presenting negative differential resistance. Our software implements deterministic and random methods to predict and explain programmability of configurable molecular arrays to perform logical, mathematical, and sensing tasks. A random method is developed to find all operation states a negative differential resistance circuit can yield. This information is valuable and would be difficult to obtain from classical circuit simulation.