Fascinating insights into sub-nm localization of molecules from Berkeley

Subnanometre single-molecule localization, registration and distance measurements

Some attention-getting work performed by Alexandros Pertsinidis, Yunxiang Zhang and Nobelist Steven Chu (also the United States' Secretary of the Department of Energy) has revealed nanoscale error mechanisms believed to be universal in CCD-based wide-field imaging systems. The work was published in the prestigious journal, Nature.

The team developed mapping and active-stabilization techniques and demonstrated that these can combine to improve the optical localization of fluorescent molecules by an order of magnitude, to a resolution of 0.5nm and an accuracy of 0.77nm. This represents a significant advance for fields such as FRET microscopy --important for observing the shape-changes of proteins, as it reveals their mechanical action and thereby illuminates the foundation of many diseases.

A key revelation in the research was that much of the microscopy system's ability to localize molecules optically was limited by high-spatial-frequency non-uniformities in the inter-pixel photoresponse of the CCD. These nanoscale errors, which appear worse at the interstices between pixels, have the effect of a finely-patterned crinkling of the pixel distribution, as if the map of pixel locations had been wadded up and then re-flattened. Since fluorescent molecules are localized to sub-diffraction precisions by calculating the center of their (Gaussian) Airy disk image as it illuminates many pixels, this non-uniformity limits the precision and accuracy of the localization.

The stabilization of the imaging setup is achieved by imaging an illuminated pinhole onto the CCD. This serves as a bright fiducial and can be localized to 0.3% of a pixel. Its position is used as feedback to stabilize the optical system against perturbation, using a high-speed piezoelectric tip/tilt mount. The locked-in stability of the system was measured to be 0.64nm over several hours. A separate feedback system based on the optical position of a selected fluorescent molecule continuously adjusts the XYZ piezoelectric nanopositioning stage carrying the test sample with respect to the optics. These continuous, sub-nanometer-precision processes place a premium on interface throughput and responsiveness.

Combining these tools, the researchers developed a method of calibrating small regions of the CCD, allowing localization of molecules to 0.5nm-- a factor of ten better than had previously been achieved. The technique can be extended to cover larger areas of the detector, up to its full extent.

Acknowledging the importance of recombinant innovation across fields, the authors note:
"...Our methodology might also prove valuable to characterize/design precision photometric imaging systems in fields such as atomic physics or astronomy... the subnanometre closed-loop control and registration afforded by our technique could become essential concepts in design of future sub-10-nm optical lithography tools and may allow new nanometrology applications."

Tantalizingly, the researchers state that in an upcoming publication, the mapping technique is extended to the intra-pixel level with approximately 1 Angstrom precision, promising another round of groundbreaking innovation and further insights into the activities of the molecular machines that underly all life.

Memristors advance

The challenge of keeping Moore's Law rolling as semiconductor linewidths dip to 20nm (only about eighty copper atoms wide) has driven such key new process technologies as nanoimprint lithography and EUV optical lithography.  It has also driven quite a few nanopositioning developments, such as positioners capable of picometer resolution plus high holding forces and active vibration isolation systems which provide nanoscale-stable worksurfaces and foundations-- essential enablers for today's most advanced process tools.

But it is also driving development of fundamentally new materials and technologies.  Graphene, a planar cousin to carbon nanotubes and buckyballs, is one of these, and is showing great promise for devising denser and faster microelectronics.

And then there are memristors, announced two years ago by HP and predicted in theory almost four decades ago by Prof. Raymond Chua of the University of California.  Coverage in the IEEE Spectrum journal was particularly informative and is the source of the following two images.

First, these astonishing nanoscale devices are regarded as no less than the fourth fundamental passive electronic component (after resistors, capacitors and inductors): 

Memristors are like resistors with memory.  Think of them as nanoscale potentiometers that can be reversibly set and read in conventional binary 0/1 ways but which are also capable of achieving and maintaining "in between" states.  Thus a single memristor only a few nanometers in extent can conceivably store many bits' worth of information, inviting a significant change in microelectronic architecture.

This means many things, most obviously some serious new competition for flash RAM and hard disks in the near future.  Now Nature reports that these devices have been demonstrated as building-blocks for logic circuitry as well.  Tantalizing recent developments by researcher R. Stanley Williams and colleagues are summarized in a recent IEEE Spectrum article,

The component’s use in computer memory was a foregone conclusion. The memristor can reversibly change its resistance depending on how much current flows through it. The researchers’ surprising new discovery is that a memristor can handle either data storage or logical computation depending on the amount and duration of the current sent through it. Three memristors can complete a NAND operation, the researchers report, so any Boolean function can be implemented if you string enough of the devices together.

Clearly, memristors herald a new chapter in semiconductor engineering, applications and fabrication techniques.  But might there be applications beyond the microchip?  A key purpose of this blog is to bring novel technologies to the attention of our diverse customer base in hopes of spurring cross-pollination and recombinant innovation across multiple fields.  Perhaps memristors will play a role in enabling something entirely new: maybe a novel lab-on-a-chip, or miniaturized autonomous dataloggers powered by piezo scavenginghttp://www.pi-usa.us/pdf/PI_Catalog_DuraAct_Piezo_Patch_Transducer_Piezo_Composite_C1.pdf, or nanoprobes with onboard signal processing and storage.  More likely, it will be none of these-- who, at the birth of the any of the other three fundamental passive circuit elements, could have predicted the computer you're reading this on?

Williams is featured in a fascinating and disarmingly casual online video describing memristors, below.

Novel approach illuminates nm-scale stabilities over many minutes

Researchers at the Block Lab at Stanford University devised a novel test which quantifies the stability benefits of long-travel sample positioning stages based on piezomotors as opposed to classical, screw-driven mechanisms. It has long been suspected that lubricant flow at the screw/nut interface would contribute to long-term settling and creep behavior and that a well-designed linear piezomotor would avoid this, but the necessary instrumentation to confirm this at the nanoscale over many minutes' time has not existed, as conventional interferometry and similar techniques are themselves insufficiently stable over the timeframes required.

Publication of the article followed the 5th Biennial Winter Workshop on Single Molecule Biophysics at the Aspen Center for Physics in 2009 and includes both an overview of nanopositioning terminology and specifications and a remarkable graph which visualizes the stability of a piezomotor and a good-quality screw-driven sample stage.

Piezo-based vibration isolation advances nanolithography

STACIS actuators supporting a photolithography scanner’s isolation platform
So many of today's essential technological wonders would be impossible without the semiconductor industry's relentless and decades-long advancements in production techniques and capabilities. Today's powerful microprocessors and digital signal processors gain their capabilities and affordability from manufacturers' ability to repetitively and consistently replicate nanoscale structures with high yield using optical lithography. In addition to controlling the alignment and position of silicon wafers throughout their processing cycle, the machinery must be isolated from ambient vibrations from machinery, roadways, natural seismicity and even people walking around.

TMC has led the industry in leveraging the ability of piezoelectric actuators to achieve nanoscale stabilities which enable the next generations of nano-lithography. In an article in Semiconductor International, this capability is described, along with critical reliability advancements which ensure that semiconductor fabs can consistently and economically crank out the products our modern lives depend on.

Announcement: PI-USA is ITAR-compliant

Many nanopositioning applications involve export-control considerations. PI-USA is pleased to note that we have instituted organizational structures and procedures to comply with ITAR requirements that often apply in these situations. Just advise your PI sales or applications engineer if your application involves export-controlled information, and visit http://www.pi-usa.us/products/ITAR/.

A close-up look at Single-Molecule Biophysics

XVIVO has composed a remarkable animated look at today's understanding of the molecular activities that go on in the living cell. This understanding is based on the quickly-evolving field of Single-Molecule Biophysics, which utilizes innovative tools such as optical tweezers and nanopores to illuminate the most fundamental processes of life: the dynamical mechanics of biochemistry. For us, this is a field which thrives at the furthest frontiers of nanoscale positioning control. It drives many advancements in resolution and functionality, and it depends on long-term nanoscale stabilities of every component in the system.

New Products: Family of USB nanopositioners with integrated, 24-bit DACs

Digital and Analog Controller Overview
Our exciting, expanding line of digital and analog nanopositioning controllers is growing every month. As ever, our aim is to provide the broadest selection for the most optimal match between product and application.  We hope you'll review our latest news on the controller front and contact your local PI applications professional to discuss your needs.
Multi-Channel Digital Piezo Motion Controllers with Dynamic Linearization
E-709 Digital Piezo Motion  Controller for Nanopositioning

A fascinating video on Super-Resolution Microscopy

One of the most astonishing and useful developments in the worlds of biology and biophysics in recent years has been the rapid advent of techniques such as Photoactivated Localization Microscopy (PALM) and Fluorescence Resonance Energy Transfer (FRET), which allow researchers to construct images with molecular-scale resolution, far finer than Abbe's classical diffraction limit allows. The field--collectively termed Super-Resolution Microscopy--is illuminating biological structures that are the fundamental scaffolding of life, the framework of disease, and the stepping-stones to cures.

The prestigious journal Nature has produced an instructive online video which provides a concise overview of this field:

More articles on nanopositioning applications in microscopy and imaging