Analysis and separation of atomic ions within a portable setting are studied in forensic applications of radiological debris analysis. Ion mobility spectrometry (IMS) may be used to show separation of atomic ions, while the related method of differential mobility spectrometry (DMS) has focused on fractionation of primarily molecular components. We set out to investigate DMS as a means for separating atomic ions. We initially derived the differential ion mobility parameter, alpha, from classic empirical IMS data of atomic ions, cesium and potassium, each showing its own distinct form of alpha. These alpha functions were applied to DMS simulations and supported by analytical treatment that suggested a means for a rapid disambiguation of atomic ions using DMS. We validated this hypothesis through the prototype cesium-potassium system investigated experimentally by DMS coupled to mass spectrometry (MS). Such a feature would be advantageous in a field portable instrument for rapid atomic analyses especially in the case of isobaric ions that cannot be distinguished by MS. Herein, we first report this novel method for the derivation of alpha from existing field dependent drift tube ion mobility data. Further, we translate experimental DMS data into alpha parameters by expanding upon existing methods. Refining the alpha parameter in this manner helps convey the interpretation of the alpha parameter particularly for those new to the DMS field.

Differential mobility spectrometry (DMS) is applied to the analysis of inorganic mixtures relevant to nuclear forensics. Three primary components of potential radiological dispersal devices (RDDs), cobalt, cesium, and strontium, were studied by DMS to demonstrate rapid sample cleanup when coupled to mass spectrometry. Nanosprayed salt solutions comprised of stable analogs, as proxies to these radioisotopes, and isobaric interferents were introduced to DMS. The DMS effluent was directly coupled to a mass spectrometer to confirm the elemental identity of the separated clusters. DMS dispersion plots demonstrated distinctive elemental separation from both atomic and molecular interferents. These results support the potential use of DMS as a means of rapid separation for inorganic analyses prior to analysis in a field portable mass spectrometer. The mechanism for this process is speculated to involve dynamics of solvent cluster formation under the influence of the alternating high and low electric fields of the DMS.

Abstract-We present a review of current implementations of nanohole array sensor technology and discuss future trends for this technique applied to multiplexed, label-free protein binding assays. Nanohole array techniques are similar to surface plasmon resonance (SPR) techniques in that local refractive index changes at the sensor surface, correlated to protein binding events, are probed and detected optically. Nanohole array sensing differs by use of a transmission based mode of optical detection, extraordinary optical transmission (EOT) that eliminates the need for prism coupling to the surface and provides high spatial and temporal resolution for chip-based assays. This enables nanohole array sensor technology to combine the real time label-free analysis of SPR with the multiplexed assay format of protein microarrays. Various implementations and configurations of nanohole array sensing have been demonstrated, but the use of this technology for specific research or commercial applications has yet to be realized. In this review, we discuss the potential applications of nanohole sensor array technology and the impact of that each application has on nanohole array sensor, instrument and assay design. A specific example presented is a multiplexed biomarker assay for metastatic melanoma, which focuses on biomarker specificity in human serum and ultimate levels of detection. This example demonstrates strategies for chip layout and the integration of microfluidic channels to take advantage of the high spatial resolution achievable with this technique. Finally, we evaluate the potential of nanohole array sensor technology against current trends in SPR and protein micro-arrays, providing direction towards development of this tool to fill unmet needs in protein analysis.