We here report on the design of a planar microslot waveguide NMR probe with an induction element that can be fabricated at scales from centimeters to nanometers to allow analysis of biomolecules at nano-or picomole quantities, reducing the required amount of materials by several orders of magnitude. This device demonstrates the highest signal-to-noise ratio for a planar detector to date, measured by using the anomeric proton signal from a 15.6-nmol sample of sucrose. This probe had a linewidth of 1.1 Hz for pure water without susceptibility matching. Analysis of 1.57 nmol of ribonuclease-A shows high sensitivity in one-and twodimensional NMR spectra. Along with reducing required sample volumes, this integrated geometry can be packed in parallel arrays and combined with microfluidic systems. Further development of this device may have broad implications not only for advancing our understanding of many intractable protein structures and their folding, molecular interactions, and dynamic behaviors, but also for high-sensitivity diagnosis of a number of protein conformational diseases.inductive microslot ͉ miniature probe fabrication ͉ nanomole RNAase-A structural detection ͉ nuclear magnetic resonance scaling ͉ ultra-sensitivity N uclear magnetic resonance (NMR) is a powerful analytical tool not only for determining complex biomolecular structures (1-4) but also for monitoring molecular dynamics (5-7). Despite its versatility, NMR protein and large-molecule structural analyses currently require large quantities of protein material at high concentration and purity (8-10), and timeconsuming data gathering (11-13). Furthermore, it has been difficult to obtain adequate amounts of proteins with high molecular weight, many protein complexes, and especially membrane proteins for structural analysis because they can form insoluble aggregates (14). We here report design and fabrication of a microdevice that can analyze nanomole quantities of proteins (15)(16)(17)(18)(19), and that can be integrated in microfabricated systems.The ultimate sensitivity limit is a single spin. Single-electron spins have been detected by using mechanical oscillations (20) and by single nuclear spins using optical methods (21,22). For a volume on the order of Ϸ10 8 spins, a report of a novel semiconductor detection mechanism shows electronic detection of small quantities of spin 3/2 nuclei at the nanoscale (23). However, all of these techniques require low temperatures. For liquid samples at room temperature, pioneering work on fabrication of solenoids around capillary tubes (16, 24) and microfabrication techniques to create planar coils on semiconductor substrates (1, 25) demonstrates that miniaturization of probes is possible and substantially reduces sample quantity while retaining signal sensitivity (15). Solenoidal microcoils detect nanomole quantities with high sensitivity but have not been successfully fabricated below Ϸ300 m inner diameter (26), whereas planar coils on semiconductor substrates are scalable but show lower signal sensitivit...

Abstract-Passive radio-frequency identification (RFID) systems based on the ISO/IEC 18000-6C (aka EPC Gen2) protocol have typical read rates of up to 1200 unique 96-bit tags per second. This performance is achieved in part through the use of a medium access control algorithm, christened the Q-algorithm, that is a variant of the Slotted Aloha multiuser channel access algorithm. We analyze the medium access control algorithm employed by the ISO/IEC 18000-6C RFID air interface protocol and provide a procedure to achieve optimal read rates. We also show that theoretical performance can be exceeded in many practical use cases and provide a model to incorporate real-world data in read-rate estimation.Note to Practitioners-Estimating read-rates in RFID has always been something of a black art. At one end of the spectrum, in the pure-theory approach, rates are estimated by taking the duration per bit and calculating the total number of bits that can be decoded per second. This approach does not take any of the protocol overheads or real-world conditions into account. In the pure-experimental approach, a standard test case is used to relatively compare read-rates as several factors-tags, readers, firmware, protocols, etc., are varied. Neither of these approaches really provides any insight into the problem of estimating read rates for the general case.In this paper, we take on this problem by developing a first-principles model of collision probability in the Gen2 medium access control layer. Collisions of tag responses are a dominant factor in determining read rates in Gen2 systems. Using this model, we show that the worst case efficiency of the protocol can be no less than 36.8%, i.e., it should be possible to see more than 36.8% of a given population of tags per unit time. We them develop a dynamic Q-algorithm that performs much better than the worst case, and show its performance relative to a static Q-algorithm.We then relax the assumptions underlying the above algorithm so as to be able to incorporate real-world situations and provide a framework wherein practitioners can make some measurements of a particular situation and use our model to estimate expected read rates. Three important factors that need to be considered are: (i) the different decoding times for different types of slot-occupancy; (ii) the capture effect, wherein a two-occupancy slot is decoded as a valid tag because the backscatter powers are sufficiently different; and (iii) the distribution of backscatter powers. We develop a model to account for these three factors.Although our models make several assumptions, we have designed and deployed readers that justify almost all of them. We are currently working on developing a deeper characterization of the backscatter power distribution of a population of tags. This will allow us to use the signal processing capability of our readers to Manuscript received July 29, 2007 disambiguate two-occupancy slots and boost read rates well-above those predicted by our model. This is the focus of our current resear...

No abstract

No abstract

No abstract