Duke University scientists, have by using enzymes from E. coli bacteria, introduced a hundred-fold improvement in the precision of features imprinted to create microdevices such as labs-on-a-chip. The inkless microcontact printing technique can imprint details measuring close to one nanometer, or billionths of a metre, the team from the University’s Pratt School of Engineering reported in the Sept. 24, 2007 issue of the Journal of Organic Chemistry.
“This has a lot of potential, because we don't have the resolution issue,” said Robert Clark, a professor of mechanical engineering and materials science and dean at Duke.
“The really important part is that with a biological catalyst there’s no ink involved,” added Duke chemistry professor Eric Toone.
In traditional microcontact printing – also called soft lithography or microstamping – an elastic stamp’s end is cast from a mould created via photolithograpy – a technique used to generate microscopic patterns with light.
Those patterns are then transferred to a surface by employing various biomolecules as inks, rather like a rubber stamp.
A shortcoming of traditional microcontact printing is that pattern transfer relies on the diffusion of ink from the stamp to the surface. This same diffusion spreads out beyond the limits of the pattern as the stamp touches the surface, degrading resolution and blurring the feature edges.
As part of the experiment, Prof. Clark and graduate student Matthew Johannes crafted a microstamp out of a gel-like material called polyacrylamide, which compresses more uniformly than the silicone material known as PDMS, which is normally used in microstamping.
For this proof-of-principle demonstration, Prof. Toone’s team chose biological enzyme exonuclease I, derived from the bacterium E. coli, as a catalyst.
In one set of experiments, the polyacrylamide stamp pattern bearing the tethered enzymes was pressed on a surface of gold previously covered with a uniform coating of single-stranded DNA molecules.
The DNA molecules were also linked to fluorescent dye molecules to make the coating visible under a microscope.
The team found that wherever the enzyme met the DNA, the end of the DNA chain and its attached dye were broken off and removed. This created a dye-less pattern of dots on the DNA coating, with each dot measuring about 10 millionths of a metre diameter.
Findings further revealed very precise microdots, as the catalyst that created them could not shift their position more than the length of its chemical tether – less than one nanometer.
“Whether the stamp was left on for a short period of time, or for days, the pattern did not change,” said Prof. Clark.
He said the inkless microstamp could also re-use the same suspended catalyst molecule repeatedly.
“Enzymes can deteriorate with extended use. But because of our tether attachment chemistry, we can easily wash the old enzyme off, put on a new one and keep going,” Prof. Clark said.
In follow-up research, Prof. Clark and Prof. Toone are evaluating more durable microstamping materials attached to longer lasting catalysts that are non-enzymatic.
They say that by using different catalysts in succession, future versions of the inkless technique could be used to build complex nanoscale devices with unprecedented precision.
“Soft lithography has really revolutionized the field of surface science over the last 30 years. And I honestly believe that using catalysts instead of diffusive processes is going to become the way that soft lithography is done in the future,” said Prof. Toone.
Wanasayansi wa Chuo Kikuu cha Duke wametumia enzymes kutoka kwa bakteria ya E. coli kuanzisha uboreshaji wa mara mia katika usahihi wa vipengele vilivyochapishwa ili kuunda vifaa vidogo kama vile maabara kwenye chip. "Ufundi wa kuchapisha kwa mawasiliano madogo bila wino unaweza kuchapisha maelezo ya karibu nanometer moja, au bilioni ya mita moja, ""timu kutoka Chuo Kikuu cha Pratt School of Engineering iliripoti katika toleo la Septemba 24, 2007 la Jarida la Kemia ya Kikaboni." "Hii ina uwezo mkubwa, kwa sababu hatuna suala la azimio, "alisema Robert Clark, profesa wa uhandisi wa mashine na sayansi ya vifaa na dean katika Duke. " Sehemu muhimu sana ni kwamba na kichocheo cha kibiolojia hakuna wino unaohusika, "aliongeza profesa wa kemia wa Duke Eric Toone. Katika uchapishaji wa jadi wa microcontact - pia huitwa lithography laini au microstamping - mwisho wa stempu ya elastic hutengenezwa kutoka kwa ukungu ulioundwa kupitia photolithography - mbinu inayotumiwa kutengeneza mifumo ya microscopic na nuru. Kisha, michoro hiyo huhamishwa kwenye uso kwa kutumia molekuli mbalimbali za uhai kama wino, kama vile stempu ya mpira. Upungufu wa uchapishaji wa jadi wa microcontact ni kwamba uhamisho wa muundo unategemea kuenea kwa wino kutoka kwa stempu hadi uso. Uenezaji huohuo huenea zaidi ya mipaka ya muundo huo wakati stempu inapougua uso, ikidhoofisha azimio na kuficha kingo za kipengele. "Kama sehemu ya jaribio hilo, Profesa Clark na mwanafunzi wa shahada ya pili Matthew Johannes walitengeneza ""microstamp"" kutoka kwa nyenzo inayofanana na gel inayoitwa polyacrylamide, ambayo hufinyangwa kwa usawa zaidi kuliko nyenzo ya silicone inayojulikana kama PDMS, ambayo kwa kawaida hutumiwa katika microstamping." Kwa ajili ya uthibitisho huu wa kanuni, timu ya Profesa Toone ilichagua enzyme ya kibiolojia ya exonuclease I, inayotokana na bakteria E. coli, kama kichocheo. Katika jaribio moja, polyacrylamide stamps iliyo na enzymes zilizofungwa zilifichwa kwenye uso wa dhahabu uliofunikwa hapo awali na kifuniko sawa cha molekuli za DNA za nyuzi moja. Molekuli za DNA pia ziliunganishwa na molekuli za rangi ya fluorescent ili kufanya kifuniko hicho kiwe kinachoonekana chini ya darubini. Watafiti walipata kwamba kila mahali ambapo enzyme ilikutana na DNA, mwisho wa mlolongo wa DNA na rangi iliyoambatanishwa nayo ilivunjwa na kuondolewa. Hii ilisababisha muundo wa dots kwenye kifuniko cha DNA, na kila dots kupima karibu 10 millionths ya mita kipenyo. Utafiti huo ulionyesha kwamba vidonge vidogo vilikuwa sahihi sana, kwa kuwa kichocheo kilichovitengeneza hakingeweza kubadilisha nafasi yao zaidi ya urefu wa kamba yake ya kemikali - chini ya nanomita moja. "Iwe muhuri huo uliachwa kwa muda mfupi, au kwa siku nyingi, muundo huo haukubadilika", akasema Profesa Clark. Alisema microstamp inkless pia inaweza kutumia tena sawa kusimamishwa kichocheo molekuli mara kwa mara.  Enzymes inaweza kuharibika na matumizi ya muda mrefu. Lakini kwa sababu ya kemia yetu ya kushikamana, tunaweza kuosha enzyme ya zamani kwa urahisi, kuweka moja mpya na kuendelea, "Prof. Clark alisema. Katika utafiti wa kufuatilia, Profesa Clark na Profesa Toone wanathamini vifaa vya kudumu zaidi vya microstamping vilivyounganishwa na viongezeo vya kudumu zaidi ambavyo sio enzymatic. Kwa kutumia catalysts tofauti kwa mfululizo, matoleo ya baadaye ya mbinu ya inkless inaweza kutumika kujenga vifaa tata nanoscale na usahihi usio na kifani. Lithography laini imebadilisha sana uwanja wa sayansi ya uso katika miaka 30 iliyopita. "Na ninaamini kwa uaminifu kwamba kutumia catalysts badala ya michakato ya kuenea itakuwa njia ambayo lithography laini inafanywa katika siku zijazo. """