Sunggook Park

We report a thermoplastic nanofluidic sensor (exonuclease time-of-flight; X-ToF) fabricated via nanoinjection molding that integrates an immobilized nanoscale enzymatic reactor (INER) directly with a dual in-plane nanopore ToF (DNP-ToF) reader, which not only uses the parameters typically used for resistive pulse sensing (RPS)─normalized event amplitude and time width─but the time taken for a single-molecule to travel between two pores in series. This platform enables the label-free monitoring of complex biological reactions at the single-molecule level. A critical hurdle in integrating such bioenzymatic reactions with RPS is reconciling disparate process step requirements, for example salt effects on an enzymatic reaction and high salt needs for RPS. We addressed this through strategic UV/O₃ surface engineering; an optimized 3.5 min dose created effectively charge-neutral nanopores that maximized capture rates while sustaining a robust ensemble electroosmotic flow (5.33 ± 0.33 × 10^-5 cm²V^-1 s^-1) and simultaneously preserving enzyme activity. To demonstrate the sensor's utility, exoribonuclease 1 (Xrn1) was used as a model. X-ToF successfully deduced the dissociation constant of an input Cas9 RNA to Xrn1 (2.4 ± 0.02 μM^-1) and monitored in real-time ribonucleotide generation from Cas9 with a cleavage rate of 23 nt/s. Ultimately, this platform serves as a highly versatile tool that can be repurposed for DNA, RNA, or protein sequencing simply by changing the identity of the immobilized enzyme.

Nanopore sensing provides an ideal strategy for the label-free detection of single molecules in a variety of application scenarios. Working under the principle of resistive pulse sensing (RPS), nanopores consist of constrictions with sub-100 nm dimensions to enable single-molecule resolution by matching pore size to target dimensions (scaling); the optimal signal-to-noise ratio (SNR) results when the electrically biased pore is comparable in size to the molecule to be analyzed. When single molecules are electrokinetically transported through such remarkably small pores, they temporarily disturb the flux of ions moving through them, generating unique signals. These signals vary based upon the molecules' shape, size, orientation, and other physicochemical properties. Nanopores are generally divided into two main categories owing to their fabrication approach and material: biological and solid state. While biological nanopores have been the dominant sensor format due to their exceptionally small size, solid-state nanopores can demonstrate high performance characteristics attributed to their rigidity, stability, and high versatility in shape, material, and configuration. This review will explore the state-of-the-art in biological and solid-state nanopores and their abilities to detect and identify single biomolecules in a label-free manner. We will also review two topographical configurations of nanopore sensors; in-plane and out-of-plane sensors. The evolution of nanopore sensing will be reviewed, starting with out-of-plane biological sensors and progressing to in-plane sensors fabricated in plastics via replication technologies.

The reliability of high-frequency chip-to-chip (C2C) interconnects requires the durability of Cu interconnects and polymer dielectric interfaces. In this study, we examine the temperature cycling performance of Cu-epoxy interfaces, including methylimidazole and amine functional silane adhesion promoters along with electroplated or electroless metal interlayers such as Ni, NiCo _0.64 P _0.25 , NiW _0.48 P _0.10 , and CoW _0.66 P _0.17 . X-ray photoelectron spectroscopy is used to determine chemical states and compositions. O diffusion is analyzed using energy-dispersive X-ray spectroscopy. The adhesion strength was measured using a peel tester, and sheet resistance was characterized using a four-point probe before and after temperature cycle tests. Insertion losses were measured using a vector network analyzer as a function of temperature cycling. Our results indicate that organic adhesion promoters such as silanes show improvements in the initial adhesion; however, extended temperature cycling results in weakened interfaces associated with Cu oxidation. The CoW _0.66 P _0.17 metallic interlayer is more durable and exhibits a minimal 0.02 dB mm ⁻¹ change in insertion losses at 18 GHz after 1500 cycles.

We are developing a unique protein identification method that consists of generating peptides proteolytically from a single protein molecule (i.e., peptide fingerprints) with peptide detection and identification carried out using nanoscale electrochromatography and label-free resistive pulse sensing (RPS). As a step in realizing this technology, we report herein the nanoscale electrochromatography of model peptides using thermoplastic columns with surfaces engineered to identify peptides via their molecularly dependent mobility (i.e., time-of-flight, ToF). ToFs were elucidated using a dual in-plane nanopore sensor, which consisted of two in-plane nanopores placed on either end of the nanoelectrochromatography column. The surface of the nanocolumn, which consisted of poly(methyl methacrylate) (PMMA), was activated with an O₂ plasma, creating surface carboxylic acid groups (-COOH) inducing a surface charge on the column wall as well as affecting its hydrophilicity. To understand scaling effects, we carried out microchip and nanochannel electrochromatography of the peptides labeled with an ATTO 532 reporter to allow for single-molecule tracking. Our results indicated that the apparent mobilities of the model peptides did not allow for their separation in a microchannel, but when performed in a nanocolumn, clear differences in their apparent mobilities could be observed especially when operated at high electric field strengths. We next performed label-free detection of peptides using the dual in-plane nanopore sensor with the two pores separated by a 5 μm (length) column with a 50 nm width and depth. When a single peptide molecule passed through an in-plane nanopore, the sensor read a pair of resistive pulses with a time difference equivalent to ToF. We identified the peptides by evaluating their ToF, normalized RPS current transient amplitude (ΔI/I₀), and RPS peak dwell time (t_d). We could identify the model peptides with nearly 100% classification accuracy at the single-molecule level using machine learning with a single molecule measurement requiring <10 ms.

Future processes and materials are needed to enable multichip packages with chip-to-chip (C2C) data rates of 50 GB/s or higher. This presents a fundamental challenge because of the skin effect, which exacerbates signal transmission losses at high frequencies. Our results indicate that smooth copper interconnects with relatively thin cuprous oxides (Cu₂O, Cu^I) and amine-functional silane adhesion promoters improve interfacial adhesion with epoxy dielectrics by nearly an order of magnitude. For the first time, we present X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy evidence of Cu(I)-O-Si bond formation at silane-treated interfaces. Thus, relatively smooth interconnects can benefit from reduced skin losses while maintaining their mechanical integrity and reliability. Failure mechanisms of Cu interconnects with cuprous and cupric oxide (CuO, Cu^II) are explored using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). These results indicate that both cupric oxides and relatively thick cuprous oxide interfaces lead to relatively weaker interfaces compared with thin cuprous oxides with adhesion promoters.

Future multichip packages require die-to-die (D2D) interconnects operating at frequencies above 10 GHz; however, the extension of copper interconnects and epoxy dielectrics presents a trade-off between performance and reliability. This article explores insertion losses and adhesion as a function of interface roughness at frequencies up to 18 GHz. We probe epoxy surface chemistry as a function of curing time and use wet etching to modulate surface roughness. The morphology is quantified by atomic force microscopy (AFM) and 2-D fast Fourier transform (2D FFT). Peel test and vector network analysis are used to examine the impacts of both type and level of roughness. The trade-offs between power efficiency and reliability are presented and discussed.

We report the generation of ∼8 nm dual in-plane pores fabricated in a thermoplastic via nanoimprint lithography (NIL). This device was used to detect and identify single rNMP molecules via resistive pulse sensing.

In this work, we explore a simplified model based on both analytical and computational methods for the study of film-boiling droplet motion on microscale ratchets. We consider a specific ratchet design with the length periods and depth of ratchets much smaller than the size of the droplet. We conclude based on our modeling that for the ratchet configuration considered in this paper, the conduction within the vapor film is the dominant means of heat transfer in comparison with convection and radiation. Furthermore, we demonstrate a more manageable two-dimensional model in which analytical approaches coupled with computational approaches yield reasonably accurate results in comparison to the actual experiments.

We present sub-30 nm nanofluidic devices via injection molding, enabling single-molecule manipulation, identification, and detection. Our work advances injection molding with UV-resin molds, simplifying prototyping by eliminating Ni mold fabrication.