Cell-culturing substrates where cell adhesion can be switched on by external stimuli during cell cultivation are useful scaffolds for tissue engineering, cell-based drug screening, and fundamental cellular studies. Here, we show a new strategy for photoactivation of a substrate for cell adhesion under standard fluorescence microscopes. A glass substrate chemically modified with an alkylsiloxane having a photocleavable 2-nitrobenzyl group was coated with bovine serum albumin to prevent cell adhesion. Upon irradiation under a fluorescence microscope, the protein was replaced with fibronectin, which made the irradiated region cell-adhesive. Subsequent seeding of HEK293 or COS7 cells produced patterns corresponding to the irradiated patterns. We succeeded for the first time in positioning single cells in proximity to cultivating single cells. The present method provides a general strategy for positioning single cells of same or different types at any locations on the substrate and will be useful for studying cell-cell interactions.

Cell micropatterning is a method for controlling the placement of living cells on a substrate surface. [1][2][3][4][5][6][7][8] It is important for a wide range of applications, such as tissue engineering, cellbased drug screening, and fundamental cell biology studies. Most cell micropatterning methods fall into three categories based on strategy: (1) seeding cells on a chemically patterned surface of different cell adhesiveness, (2) seeding cells on a topographically patterned surface, or (3) directed delivery of cells onto discrete regions of a substrate. Although the latter two categories are also important, this review mainly focuses on the first category. This is because it is the most common strategy and it provides tools to study fundamental aspects of cell adhesion at the single protein/receptor molecule level. 9There are excellent reviews that also cover the latter two categories. 3,8,10 We first introduce some of the important applications of cell micropatterning in general. We then describe methods for micropatterning the cell adhesiveness, referring to materials that promote or inhibit cell adhesion. We then move on to much more sophisticated substrates, so-called "dynamic substrates", whose cell adhesiveness can be changed by an external stimulus, such as heat, voltage and light. As an example of dynamic substrates, we describe a caged culture substrate developed by our group. This type of functional substrate opens up new possibilities in bioanalytical and biomedical sciences. Cell micropatterning is an important technique for a wide range of applications, such as tissue engineering, cell-based drug screening, and fundamental cell biology studies. This paper overviews cell patterning techniques based on chemically modified substrates with different degrees of cell adhesiveness. In particular, the focus is on dynamic substrates that change their cell adhesiveness in response to external stimuli, such as heat, voltage, and light. Such substrates allow researchers to achieve an in situ alteration of patterns of cell adhesiveness, which is useful for coculturing multiple cell types and analyzing dynamic cellular activities. As an example of dynamic substrates, we introduce a dynamic substrate based on a caged compound, where we accomplished a light-driven alteration of cell adhesiveness and the analysis of a single cell's motility.

A drop in melting point of 21.5°C is induced by the UV‐photolytic trans→cis isomerization of the duplex formed between an oligonucleotide bearing two D‐threoninol‐tethered azobenzene moieties (see picture) in the side chain and its complementary counterpart. On irradiation with visible light, the dissociated single‐stranded oligonucleotides regenerate the duplex.

Oligopeptides are efficiently hydrolyzed by Ce(IV) to the corresponding amino acids under mild conditions. The pseudo first-order rate constants for the hydrolysis of H-Gly-Phe-OH and H-Gly-Gly-OH at pH 7.0 and 50 degrees C are 3.5 x 10(-1) and 2.8 x 10(-1) h(-1), with [Ce(NH4)2(NO3)6]0=10mM (the half-lives are 2.0 and 2.5 h). The catalytic activity of the Ce(IV) is far greater than those of other lanthanide ions and non-lanthanide ions. No oxidative cleavage was observed under the reaction conditions. Catalytic turnover of the Ce(IV) was also evidenced. The hydrolysis is fast especially when the substrates have no metal-coordinating side chains. Tripeptides and tetrapeptides are hydrolyzed at the similar rates as the dipeptides. In the hydrolysis of tripeptides, the amide linkage near the N-terminus is preferentially hydrolyzed. Neither the N-carbobenzyloxy derivative nor the amide of H-Gly-Phe-OH is hydrolyzed to a measurable extent, showing that both the terminal amino group and the carboxylate are coordinated to the Ce(IV) ion. This complexation is further confirmed by 1H NMR spectroscopy. The Ce(IV) ion is therefore one of the most active catalysts for peptide hydrolysis.

Spatiotemporal control of cell migration was achieved on a photoactivatable cell-culturing substrate. Single cells were micropatterned on the substrate and were induced to extend protrusions led by lamellipodia or filopodia alternatively by the subsequent formation of wide or narrow paths in their surroundings, respectively. By tracking the migration of single cells in a microarray format, we performed quantitative analysis of the migration rates of single cells.

Colorimetric detection of mercury ions (Hg(2+)) with the naked eye was accomplished within 1 min by a combination of non-crosslinking aggregation of double-stranded DNA-carrying gold nanoparticles and complex formation of thymine-Hg(2+)-thymine.

Methyl Red H aggregate of predetermined size is successfully synthesized from the DNA conjugate involving multiple Methyl Red moieties in sequence. In the single stranded state, hypsochromicity monotonically increases with the number of incorporated dyes: the peak maximum of the conjugate involving six Methyl Reds appears at 415 nm, and the shift is as great as 69 nm (3435 cm(-)(1)) with respect to the monomeric transition. This large hypsochromicity accompanied by the narrowing of the band clearly demonstrates that H aggregate is formed in the single strand. H aggregation is further promoted at higher ionic strength. Upon addition of complementary DNA below the T(m), however, this H band disappears and a new peak appears at 448 nm, indicating that aggregated structure is changed by the duplex formation. This spectral change is completely reversible so that the H band at 415 nm appears again above T(m). Thus, aggregated structure can be reversibly controlled by the formation and dissociation of the DNA duplex.

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